Hi.
First of all, thanks for the latest additions to NGUI, I'm loving the post 3.0.0 features.
So, I updated our project from 2.x.x version to the latest 3.0.3c and I do realise that it's not a stable version but I wanted to report this bug if it was not known yet.
Previously I had no problems with leaving the play mode on while I edited my scripts. And when I was done editing, I would return to Unity, stop the play, and press play again to test new changes.
But after the 3.0.3c update Unity crashes every time I do this.
Of course it would be smart to stop Unity before changing the code but I guess the habit of leaving the play mode on while looking(and editing) the code, is buried way too deep into my brain because I've had 10 crashes already this morning.

Cheers.
Edit:
And to be exact, Unity does not crash on the "Compiling scripts" phase, but a phase after that, which seems to just flash so quickly that you don't have time to see what it is.