They still haven't fixed this?!?!???
You can try to submit bug reports, but I'm afraid Adobe isn't taking this very seriously. I spent countless hours writing bug reports, forum posts, not to mention reproducing the bug alongside tech support. They said they would fix it 5 months ago!! This is such a critical problem! Come on Adobe, get it together already. If we can't create masks, then it's impossible to professionally grade our footage.
For now, I suggest using the industry standard application, DaVinci Resolve. It's infinitely better, not to mention FREE.
In case you're interested, here are a couple of my previous threads on the issue:
https://forums.adobe.com/message/6245538#6245538#6245538#6245538
https://forums.adobe.com/message/6247527#6247527#6247527#6247527