Okay it seems that I found out the cause of it. If you maximize the MDI window(s), and switch the active window to a channel with unicode characters in the topic, the translucent effects disappears. This only happens when there's unicode characters in the titlebar, for all other channels/windows with titlebars that didn't contain any unicode characters the bug doesn't happen.
Note. If you set a topic with unicode characters, you have to switch to another window and back before the bug occurs.
