This is just plain old terrible programming.
When creating a new bin, the bin window appears in avid, but the new bin itself does not appear in the project window. If you close the new bin's window, it still won't appear, and effectively is lost to Avid. What could possibly be going on?
Looking at the Finder level, I can see that the new bins were created without ".avb" at the end of their names. If I manually add that extension, lo and behold the bins appear in the project window!
But what's causing these bins to be created sans extension? Some crazy bug? Some horrible computer virus? Nope. Just dumb fucking Avid.
This problem is the result of turning on the option in the General Settings to allow for filenames longer than 27 characters. For some reason, Avid takes this to mean "stop properly writing bin names." Turning that option off again fixes the problem.
Dumb. Fucking. Avid.
Seriously did no one testing this software turn on the option that allows you to make bins with longer filenames and then - I don't know - try to make a fucking bin???