Powershell ISE locks out ALL scripts while one script is being debugged. This makes life unfun, but has an easy workaround. Opening a second ISE allows the other script to be debugged, but this would mean that I would need to open an ISE for every script I am working on (I can easily find myself working on three scripts). I base my opinion on this being a bug because I use VBSEdit, PowerGUI, and Visual Studio and none of them exhibit this behavior (although the only pertinent one should be VS). I also hear that Sapien does not exhibit this behavior. Given all that I would think that this shouldn't be a by design (I would find it odd if someone specically designed the program to lock out other scripts, but that is just my .02).