I discovered this in SLua where adding and removing handlers is a regular feature, but I was able to reproduce it in LSL using state changes for the same purpose.
!!!Substantially more info in the Environment, Details, and Steps to Reproduce fields, but those don't seem to be visible to anyone but me, and I supposed the privileged LL users. Useless for other user review, but when I try to post with everything here, I get an error. I'll add the other fields as comments so that others can see them until this gets fixed. (I suspect somebody is actually working on the canny system as I type, due to the changes I see as when I reload.)!!!