I see what you mean. It happens now, and didn't used to. And I agree that it's a bug. Probably the best thing to do is to submit the problem here:
Photoshop Family Customer Community , which is the official Adobe place to submit bug reports.
Thanks. I've submitted this as suggested.
It looks like the bug started back with LR2015.1 and is in each version since.
My backup files prior to and including June 7th 2015 are ok but the June 16th one and all the ones after that have the "T" attribute set for the zip file.
(LR 2015.1 was released June 15th so LR2015.0 was ok.)
I could not find your post on the feedback site to add my +1 vote.