I have experience this on occasion as well. What I have found is that if I have an entity selected in the block, while still in the block editor (like a pice of text or line), and I hit "close block editor" then it will lock up. I have developed the habit of hitting the escape key a few times before hitting the "close block editor" button. This has stopped the locking up issue for me. cant explain why, but it has fixed the problem.
I have not been able to reproduce this. Does it happen with all drawings? If not are the drawings from a previous release? Please try the following solution for corrupt drawings.
Let us know if that helps.
Have you been able to resolve this problem?
I am having a similar issue with the text editor. When it happens, I can make or undo changes in the text editor, but I can't close the text editor short of closing AutoCAD with the task manager. I do seem to be able to save the changes, but have to restart the program