Thanks for the bug report, unfortunately I have not been able to reproduce this issue here so far. How are you checking whether all of the lines have been written to the file? I tested using the following steps:
1. Place mirc.exe from v7.12 in an empty folder.
2. Place an empty mirc.ini in the same folder.
3. Run the mirc.exe file.
4. Fill in my nicknames.
5. Connect to a server using /server irc.efnet.org
6. Open a query window using //query $me
7. Send several messages in that window.
After each sent message, I open the log file with a text editor, and all of the lines are there.
