Let me be clear, my proposal is this:
ON ^*:OPEN: should not trigger for self-opened query windows. Only ON *:OPEN: should trigger.
Since these /halting flood/spam control scripts make use of ON ^*:OPEN:, this will maintain backwards compatibility for 99.9% of existing scripts-- certainly all the ones I've seen, and all of the ones that were listed here.
As a backup, I wouldn't mind the ME: prefix, but I think simply not triggering the haltdef'd open event effectively avoids the problem.