The one with the keyboard not responding apparently happens when ZC has been running for a long time, I think.
As did I, however, I set up some ZC threads on Friday, each running 1st.qst.
First, I let each run for a full day, unpaused. No issues.
Next, i played through level 1 using each. No issues.
I let both sit (unpaused) over the next day, and still no issues.
Next, I will pause each, and see if I can trigger this problem. In fact, I am pausing both as of this post, and I will check on them in 12 to 24 hours.
I'm trying to narrow down a way to reproduce the issue, with 2.50.2, and 2.53.0 beta 2 running simultaneously, to see if one locks up, and the other does not. This test is on Windows 7, running in windowed mode.
I still suspect script corruption in this Rainbow Death issue, as both Saffith and I mentioned, it is possible to write to some memory areas that should not be accessed by loading invalid FFC IDs. The written values may affect nothing for a long time, but they could stick around lurking in the background, and persist through quest loads, if the areas that are corrupted are not cleared on quest init by ZC.
I'll try to bound ffcs for 2.53.0, and future builds one way or another; or DD might do it. We have a bit of an ongoing debate on the best way to do this over on AGN at present.