Comment 3 for bug 699104

This occurs because the DRC runs in the main thread.

Because the DRC actually changes the state of the data during the DRC check (e.g. lines change size, flags are modified) we cannot allow the user to interact with the layout while it is running.

I think the simplest solution to this problem is to create a dialog while the DRC is running that indicates which test is being run and how much time has elapsed. This essentially tells the user "hey, I'm busy doing this work right now, come back when I'm done".