Drag the review toolwindow group from default docked position to a floating window. Size the window to about six inch by six. Drag the references thing out of this to be its own floating window. Go back to the preview window, click on preview <-> build tabs. The titlebar doesn't update. Click on message list tab, the vertical size of the window gets halved. This is reproducible. You don't actually have to drag the refs toolwindow out either.