Calendar sync deleted iphone calendar and replaced with "On my mac" cals

Similar problem..
Denied 4.0.1 update to ensure my calendars made it from my iPhone to my mac..

Only to find they all disappeared, nothing in the backup. Lost my entire shift schedule and then some.
Calendars can't sync both ways WHY? I honestly hope to god I remember when I work this week. This is a nuisance that should have been fixed a long time ago.

Now I'm upping to 4.0.1 anyway and going to try to restore next month from memory. No JB, no hacks everything is factory... Thanks a lot

Same exact problem--got my new iphone, synced it up...and promptly lost all the events I had put in to the phone. They were replaced by all the things I had in my old calendar ("don't forget trash day!", etc) rom my computer, which I never use, since let's face it, plans are made when I am NOT sitting at my computer, out in the real world.

So now I have nothing on my calendar. Looked for the box to "upload iphone events to ___" folder, like it has for contacts, but no such luck.

So how am I supposed to use my iphone for a calendar if every time I sync it, I lose everything? Someone please explain if I am missing something!

I've also had similar problems. I do believe though that my phone was syncing with my computer and replacing the information on the computer before I installed the new OS4 for the iPhone. I know I used to at least keep my info on my phone without its being erased by my info on my computer. If anyone knows how to fix the problem, I would definitely be grateful.

I'm having exactly the same problems here. I just got my iPhone 4. All's great except this sync thing.
I use my phone to enter contacts and calendar dates, but when I try and sync it all goes to what my computer has in it, which is completely annoying considering I had to sync to update from the iPhone 3 to the new one...
This only happened with this update. Anyone have any ideas what's going on? I definitely do not have the 'replace information on this phone' option selected.

Hi just went through the annoying 15 minutes registration process to post that I am having the same problem with iphone 3gs and ios4.
No amount of resetting the Sync history or unchecking overwrite iphone will prevent deleting all the calendar data on the phone. I have a backup that I can restore but the calendar is deleted after syncing again and again and again.
the notes and contacts are not deleted. I have tried creating a new outlook profile to no solution.
Haven't tried creating a new windows xp login account yet as I am not looking forward to going through all the re-installations. Any chance this significant bug will be fixed in a reasonable amount of time?
The ideal/logical solution would be to have the ability to set overwrite outlook in the itunes and not just the other way around.

Hi again,
a quick update:
*- Started a new xp account
*- synced
*- clicked on merge..
*- the iphone calendar was deleted again (IE. replaced by empty outlook calendar)

Me too. I'm working from a Mac and had synced all my gmail calendars. Now they disappear each time I plug in the Itouch to sync music etc. Wow, this IOS 4 is a nightmare. Anyone found a fix yet?

No fix yet. Apple needs to fix this very serious issue ASAP.

NEED HELP, TOO! Same problem, with 3G. The existing iCal-Data does overwrite all newer files on the iPhone! That's really great; tried it twice. No chance. Notes were sync'd correctly. But not iCal! It cannot be true!

Sigh - exact same thing here.

Same problem, struggled with this alot yesterday and had to restore from the backup like 5 times cos no matter what i did i lose my calenders in the phone all the time 😟
Now i always take a manual backup of the backup, i dont trust the iTunes cos suddenly i will have a backup of a "to new" update and alot will be gone.
Here u can see where iTunes puts the backups if u wanna do the same.
http://support.apple.com/kb/HT1766

Work around:

I had the same problem, albeit on a PC and using Outlook. For some reason, iOS4 is confused about the calendars and if it doesn't find an existing calendar on the computer that matches the naming on the iPhone, it deletes the iPhone calendar.

Anyway, I signed up for the free MobileMe trial and then synced my iPhone to MobileMe. Finally, I synced MobileMe to the calendar program (Outlook for me). This is the point that I figured out that there is a problem merging the calendars, because MobileMe created a new calendar in Outlook. Anyway, I merged the two calendars, res-ynced to MobileMe and then when MobileMe pushed, I had a good calendar on my iPhone.

Finally, I turned MobileMe off on the iPhone, added an event in the iPhone calendar and then used iTunes to sync to Outlook. Viola! Everything worked, finally.

A bit of a hassle, but it worked and now I can delete the MobileMe account so that I don't get charged, although, I think I'll run the trial a bit longer because there are some other features I may want.

Let me know if this helps.

Same problem, due to the fact I had to change my computer, as expressed in a post yesterday.

I use MobileMe as said in the previous post, thanks to MX727, it solves temporarly the problem.

However, I'm loosing trust in Apple System, first because the applications are too slow (calendar and contact are responding 5 times slower than equivallent apps in my 11 years old "Psion 5mx" ! ! ! ), then because the risk to loose datas as calendar entries is UNACCEPTABLE in a professionnal use.

I hope Apple will fixe this problem ASAP.

Exact same problem as those listed here. My Mac had to be sent back for repair because the hard drive crashed. After getting the Mac back and restoring my normal data, I resync'd my phone and had it wipe my calendars out on the phone.

Unfortunately, this has been a problem for weeks now and the calendar data is newer with MANY updates. The iPhone is the master and I can find no way to get it out. I agree, Apple has to fix this somehow. Supports recommendations failed and frankly I'm sick of restoring.

I'm going to try MX727's recommendations as a work around but Apple really needs to make it possible for us to choose the iPhone as the master during an initial sync with iTunes. At the very least, please don't WIPE OUT ALL THE DATA without some sort of warning!

Apple - where is the fix for this?

Same problem, trying a backup now hoping it will restore the calendar on my iPhone. Think I'll just give up on trying to sync calendars, can't imagine what the point of an option like this would be with something built in that will just erase months of data.