As @andreyvb reported in another thread:
Yes; I have this happen constantly. I’ll have the controller and descriptor both open for multiple screens as well as several entities and such; basically what you’d expect as a normal workflow. Switch back to the descriptor which was in designer mode…and the screen is blank. What I do is close the descriptor tab, switch to the controller’s tab, hit the descriptor button to re-open the descriptor and it’s all fine. Just a little annoying.
Also, the new buttons over on the top right that allow you to switch from designer to XML and such…they disappear pretty often. To fix, just close and reopen the descriptor.
These bugs are cosmetic but definitely cause a little slowdown in one’s work.