Thanks for your bug report. I have not been able to reproduce this issue so far.
Can you describe a step by step method that reproduces this? For example, here is how I am trying to reproduce it:
1) Run mIRC
2) Maximize the status window.
3) Connect to a server
4) Join several channels.
5) Click on the switchbar buttons to switch between windows.
In addition, please run this command in your status window:
//echo -a $os $version $beta $md5($mircexe,2) $file($mircexe).sig $alias(0) $script(0) $dll(0) $com(0)
and post your results in a reply.