Sorry, I should've mentioned that, but my Calendars were in 'iCloud', not 'On My Mac', and have been for some time.
[EDIT] Oh, and I had this happen to me while I was out and about: I left the aforementioned appointment in the Calendar on iCloud, and it eventually pushed down to my phone.
Unfortunately, the same cannot be said for iCal, as nothing has updated; it's still a barren wasteland, even with the refreshed iCal CalDAV account.
Sorry, I refer to it as "iCal" constantly, but I'm running Mountain Lion 10.8.2, as stated in the OP.
I did check iMessages, and everything there is flowing normally; even that lapse in time of conversation history with the girlfriend was pushed through to my Mac.
Reminders, however, still remain blank.
Everything is now working, except Calendars from iCloud to Mac, and vice versa.
I did end up exporting calendars from the Mac side, and deleting all calendars from iCloud. Eventually, my iPhone and iCloud were on the same page, but here's the weird bit: even thought I deleted all calendars, every calendar reappared, but empty, save for two ('Work' and 'Personal').
I've signed out of iCloud on my Mac, then signed back in, but using my alternate @me.com email address already associated (I've seen this mentioned in another, similar article). That didn't work.
From my understanding, Calendars and Reminders are handled under the same instance (since it's labeled as "Calendars & Reminders" under System Prefs > iCloud. Why would Reminders sync, but not Calendars?
OK, this is getting pathetic:
iCloud and my Mac are now talking on all fronts, but rather than iCloud pulling Calendar information from my Mac, it's pushing all the empty data to the Mac.
I have a Calendar backup (thank Thor), and whenever I import that data, iCloud decides to write over it instantly.
I've gone to iCloud, and deleted all calendars that I can. I reimport the calendars on the Mac, and iCloud simply pulls the calendars themselves, but leaves the events behind, then it's deleted from my Mac.
How do I get Calendar to push the event/calendar information to iCloud, rather than iCloud pull calendars, then deleting events?
I have the solution! No thanks to anyone, with the exception of pvonk, who at least attempted:
- Export individual calendars from Calendar using Export > Export... (I created a keyboard shortcut using ⌘ + E). Do not export as Calendar Archive; this carries with it iCloud data, which you don't want.
- Once each calendar is exported, sign out of iCloud in System Preferences, and have it delete everything; Calendar will remove the 'iCloud' section of calendar data.
- Reboot (yes, you must reboot).
- Once back, Import (again, keyboard shortcut == ⌘ + I) each calendar individually, and make sure to choose 'New Calendar' each time. They will appear under the 'On My Mac' header; this is what we want.
- In iTunes, sync your iDevice (I only have an iPhone 4), but under [Info], choose to 'Sync Calendars' and opt for 'All calendars'. This will wipe the iPhone of all calendars, since there's nothing in Calendar. You may have to do this step with each iDevice you have synced to your iCloud account, but I don't have a secondary one to test.
- Once the sync is done, go into your iDevice, and disable Calendars via Settings > Mail, Contacts, Calendars > Accounts - iCloud.
- Choose to delete the data.
- Re-enable Calendars, and choose to Merge.
- This will push all the calendar data to iCloud, which will prevent it from pushing empty data, overwriting perfectly good data on the Mac/iDevice.
iCloud (optional, but advised)
- Log in, and go to Calendar. You aren't doing anything, but sitting back and watching delicious calendars and events get pushed from your iDevice to iCloud. This also allows you to ensure your iPhone is pushing the data.
Back to the Mac
- Sign back into iCloud via System Preferences.
- Calendar may kick back an error, saying it can't connect. Dismiss this - you may have to click the yield sign next to 'iCloud' - and it should sync.
- In iTunes, there's no need to disable 'Sync Calendars' under [Info] for your iDevice; this is taken care of when you sign back into iCloud and opt for calendar syncing.
And boom. There you go.
To solve this entire issue, that Merge option on the iPhone should exist on the Mac. Rather yet, iCloud should pull new data, not overwrite it.
Apple. Fix this. I don't want to spend days figuring this out. If I didn't have an iPhone, I'd be royally screwed.