Well, it appears that they have fixed it again. I just posted the following in reply to the announcement by a QB Team member in another thread:

Thank you, Mich_S. I tried an attachment just now and can confirm that it is indeed working correctly again.

Is it going to stay fixed this time? As you have alluded to, any files that have been attached during the "bug" period will have to be deleted and re-uploaded if we want them to exhibit proper viewing behavior. I have not been attaching any files but instead saving them up in the hope that this would be fixed again. Now it will take me half a day to upload all of those. I shudder to think how much work this will be for more serious users who have dozens or even hundreds of transactions a day.