I believe Sat pointed out that ths problem here is not due to a bug, just a limitation of how log files work, maybe a design flaw, depending on your point of view. So really, there's nothing to fix, just more features to add. It's important to point out, though, that /filter -z is not the "feature to add", here, so your request isn't going to happen until mIRC's logging mechanism undergoes the improvement Sat described above.
