No. Related to it, but not the same issue.
The highlight for mIRC's active window is usually removed the moment mIRC is in focus again. I was pointing out that this doesn't happen if you close a window you didn't open yourself, e.g. an IM window popping up when someone messages you.

Normal behaviour:
- mIRC is active
- you open some other application
- you close that app so the previous one (mIRC) is active again
- highlight for mIRC's active window is removed

Inconsistency:
- mIRC is active
- some other application opens a window by itself
- you close that app so the previous one (mIRC) is active again
- highlight for mIRC's active window is not removed

Hope it's clearer now.