The scripting is very likely the cause of the issue. If I remember rightly, I changed the way /haltdef works in mIRC 6.31 so that it blocks all both sounds and speech.
The reason for this change is that in previous versions of mIRC the /haltdef command was inconsistent - it stopped sounds and speech for some events but not others. So I changed it to be consistent across all events.
The solution would be to add your own /speak commands for the particular events you are halting, as described in argv0's post.
