Okay I was able to reproduce this one and it completely freezes the engine, it sits using CPU but its completely unresponsive and when terminated it just disappears.
Reproduction steps:
Hi Daniel,
I wasn’t able to reproduce this in beta4 or @head by trying to dock the Blueprint Debug window (The one summoned from Window…Debug in the blueprint editor) into the blueprint editor. Could you confirm which window you were snapping?
A bit of background about why most of the editor is frozen while stopped at a breakpoint: we actually are paused deep inside the game thread, and are ticking the UI in a special loop to keep the debugger responsive, but have to disable anything that could re-enter the game thread.
Cheers,
Michael Noland
Yeah Im actually very impressed that the editor can even get that far honestly so you guys must have some real black magic going on there 
The editor itself though isnt just frozen its unresponsive, that window doesnt come back and nothing is clickable.
The window I was snapping is the Blueprint Debugger window, maybe its got something to do with the blueprint itself. Im in event graph of a character, I can reproduce it using a breakpoint just after event OnLanded, it does seem slightly intermittent though.
Okay I just testing snapping the main Character Blueprint window around as well, it doesnt seem to happen on the first suggested snap but if you move through them. It is fine if I normally just drag a tab around over the entire UI rapidly.
Hi Daniel,
We have successfully reproduced this issue and I have created a report. We will be investigating the cause of this issue internally now. Thank you for your report. If there is anything else that is behaving incorrectly, please let us know.
Thank you,
Alexander
