[JKT]

This isn't anything new. It has been happening since Exposé first arrived on the scene in OS X and occurs when you invoke it just as you show a new drawer (e.g. as you open a new window or Workspace) in OmniWeb; the OS probably gets confused into thinking the drawer is a separate window to the one it is meant to be attached to. To get it back into place, just hide and show the tab drawer.