Quickmask feature change

Hello. I like to  use quickmask to refine selections, and one of my favored tools was being able to use a hard-edged brush at one end of a selection's straight line, and holding down the shift key, click at the other end of that straight area to connect the selection areas with an edge that was also straight; now, however, I can't get that feature to work. Is there some setting that has changed or that I've changed that has disabled that feature, becuase I'd really like to use it again. Thanks!