I finally figured out one reason why the yellow triangle appears and locks up IMAP email accounts.

It seems that if an email comes across with any special characters in the subject line, my Pre will lock up that email account and the yellow triangle appears. The only way I can free up the Pre is to access the specific email account via Outlook or web-based email to delete the offending note. Once that's complete, the Pre will update without a problem.

I'm able to identify the specific email based on using the timestamp the yellow triangle displays as the last time the account was updated.

Hopefully this gets corrected. Here's examples of special characters: