Thank you, Niel and John!
Maybe it will get fixed in a later version.
In the meantime, selecting the columns explicitly, using SQL+, or doing John's schema browser data table workaround will all suffice. It's just unfortunate as I don't know there's an XML type column in the table until it crashes TOAD so any work I had going in my other sessions and tabs because inaccessible.
Good to know that it's not just me, though! Thanks again.