Ok, I finally
caught the bug on video, I reproduced on two different machines, both running with 7.49 and win10, with a system uptime of 7h+ and mIRC uptime of 1h so it does not require mirc to be running for a long period of time. I didn't try on a clean mIRC because I use a script to get these lines into the window anyway, both scripts are using a COM (to create a strawpoll) and a dll: dcx.dll, I'll try with a clean install and just this script loaded in the future.
Edit: when the bug occurs, I figured that if I right click the treebar, uncheck the 'lock' item, the bug goes away.
