Thanks for your response, forum hero!
1. Already tried /fupdate, no noticeable effect.
2. No antivirus running, same situation.
3. Using mIRC v 7.63 now. The situation has been the same for many years though, and I keep mIRC updated
4. Good idea, thanks! I will try that and report the results.
I also tried switching fonts around, after reading something about problems related to that. Didn't seem to help though.
