Well all I can say is what I've said in my previous post. Since the fix I've used this help file via my alias in combination of running the mIRC help file alongside it more than 200 times, probably in various order of opening, without any problem, until two days ago.
I would prefer if you were not reverting the fix for now, as I'll probably update to from 7.77 to the next beta to play around more with it on lastest version. You can eventually revert the fix in the next stable release if nothing great comes out of it.
That being said, the link to the fix in your previous post definitely seems confident in the fact that using topic instead of context id makes the bug go away. You mentioned a minimal implementation of it, could it be that mIRC is still using context id in some cases?