Can't say I have, but I don't use IMAP. The issue was reported for the Xoom, but I'm assuming you're having the same issue on the Atrix?
If so, have you tried to delete the account and reinstall with the automatic setup? It seems it only happens if you have to enter the settings manually; or do you not have that option?
If you're having the issue, you might want to make sure you file a report at the same site specific to the Atrix. I don't know if they've fixed it for our next OTA or not like they've already done for the Xoom.