Thank you, Juan. On further reflection and testing, I think this occurred with the crashing that I was experiencing (adding the script, but then PI crashing without quitting normally). It is behaving normally now. My apologies....
On another note, I have been able to *sometimes* re-create a crash I reported in the Bug forum by having an ArcsinhStretch preview window open, tracking it in HT and then trying to adjust the black point in HT. Twice in a row it crashed as soon as I touched the black point, but now I can't get it to do it again.... I'll report back if I can figure out how to crash it every time.
Mike