Bump and an update...
I had my cust return her iMac to her local Apple Specialist as they also sevice Apple hardware and they ran Apple diagnostics and confirmed all hardware is OK and confirmed no 3rd party is causing this.
The service shop reported after 5 days of testing the strange cursor issue occured BUT get this; when it appeared the area it erased revealed the login screen? ie imagine your desktop was a scratch off lotto ticket surface and you scratch off the center of your screen and doing so reveals a piece of your user picure, you move the cursor some more, 'rubbing off' the desktop from the center and you begin to see more & more the the login screen. THIS IS WHAT THE SHOP SAW AND DID when they experienced the problem.
pause..rewind...She also complained (which I forgot to mention) that the OS randomly logs her out soon after the strange cursour erasing thing.... fast forward, play...
She told the shop of the log out issue as well so all they did after seeing the issue for themselves was uncheck 'log out after n minutes' and the issue didn't reoccur and gave her back her Mac.
I don't know if she has experienced the issue since but I think this solved it.
This is still a mystery to me and I've seen a lot of Mac issues, I still think there's a bug in the graphics, the OS or something, a preferences?
i have the log of the time it occured and will post later but my eyes couldn't find any culprint when I check it.
Expert or Apple Enginner level techs out there...Any advice on why this is happpening?
Message was edited by: pgonzalez
Me too.... exactly same problem....
First my 2008, 24" iMac running 10.7.4. Yes, I had the
'log out after n minutes' checked, so let's see if it fixes the problem with it unchecked.
Then, I used migration assistant to move everything over to my new 27" iMac (2012).... and bam!!! Not cool! It's doing the same thing on my new machine!!
I've deslected the same "log out after..." so we'll see if it fixes the problem on both machines.
I think the answer is here:
It looks like this occurs when you have the machine set to log you out after a period of inactivity but the screen has gone to sleep prior to this.
The suggestion 2 in this link did not work for me.
I set display sleep to 6 minutes and kept logout time at 5 minutes but still grey square and trace appeared.
Also, there is no way, as suggested in the 1st paragraph of the article, to find the login screen with user icons.
However, I closed the lid and re-opened it. Login screen appeared and I could login again and things are back to normal.
Nonetheless, as a matter of courtesy (only), I rated this article 3 Stars.
Hope the above could be of help.
I'm having the exact same problem with my MacBook Pro. After it got infected with some malware or a virus I did a complete and total drive wipe. I started from scratch with a new download of Mountain Lion and the used Migration Assistant to reload applications. This problem started immediately after the migration, though eveything else seems OK now.
None of the suggestions above have worked for me. I've been a diehard Mac user and Apple evangelist since 1989 and this is only the second instance in all those years I've had to wipe a drive and start from scratch, but this one has me flummoxed.
It just might be time to buy one of those cheap ChromeBooks, as I've already lost way too many valuable hours trying to fix this issue and there seems to be no answer in sight, nor support response from Apple on this one.
Yes, I've done that along with the few other things recommended here. This is really killing me, and it's a shame because something as basic as this would NEVER have been released if Steve Jobs was still around. You'd think with the thousands of employees Apple has this would have happened to someone in pre-release of Mountain Lion, and that they would have fixed it before shipping.
Then...there's the whole issue of not monitoring these discussion boards so that they could at least provide a response. Thousands of employees and no one responds? Additional thousands of employees in Apple stores worldwide and no response from any of these "Geniuses"? What Apple needs at this point is a few "Damage Control Geniuses".
I'm emailing Walter Mossberg and some other tech journalists I know personallywith a 10 seciond screen grab movie of this fatal effort on Apple's part. People should know that Apple is now letting stuff like this slip past the QC Control team in the name of "ship it now, get it out the door, get the money rolling in. We'll deal with it later." That was always the Microsoft way of dealing with things, and unfortunately that way of thinking has now insidiously crept into the Apple core mindset as well.
Such a shame.