I have found out exactly why this happens for you to simulate.
Start mucking a heading, before the muck is complete click on your bolter, click new task, bolt, then wait for the heading to be completely mucked out, then click on the heading to bolt it.
What I believe happens is when you click bolt it saves the state of everything on the screen for recognition of its state, when you click on a heading that wasn't completely mucked it registers as "I can't do that" when you press ESC to try again the game completely locks up and you lose everything.
Being patient and careful with my bolters I played last night for about 3-4 hours and had the top two levels completely developed without any issues until i experienced a completely different freeze glitch.
I hope this helps, honestly though with a saving/resume playing option this is hardly a problem that really needs addressing :)