This was working prior to 2.1.2 release (June 28 2007 code). This is frequently enough under IE6. works OK under FF. The detail steps:
When we 'Untile' a portlet window to resize it (drag the lower right corner with left mouse button down), after release the left mouse button, sometimes it released (i.e. I can use my mouse to do other things in the portal window), sometimes, the underline portlet window 'sticks' to the mouse and the portlet window is still resizable (i.e. the portlet was following my mouse pointer around the screen without me clicking & dragging). I was able to get out of this situation (free my mouse pointer) by clicking my left mouse button more times.