I am running mIRC 7.19 on Ubuntu using wine. When I minimize a chat window within mIRC it shows an icon at the bottom of the mIRC screen instead of minimizing to the treebar. When I was running mIRC 6.x and minimized a chat window, the window minimized to the treebar. I attached a pic showing the minimized window icon in mirc.

This change is by design. It was one of 20+ changes that were made in mIRC v7.x to accomodate issues in Wine. In older versions of mIRC, minimizing/hiding an MDI window under Wine would result in the text label of the minimized icon being displayed. Since Wine is unable to hide this icon, the new version of mIRC displays the graphic icon along with the text label for aesthetic reasons.