It's a problem that's not been resolved. Worse still, in some instances the adhesive can gradually seep through to the printed surface of a stamp, damaging it...
Thanks heathfield for a very informative link. I'm still intrigued by what you do with stamps that can't be removed from envelopes with water? For example - 1st. class stamps have little cutouts that get left behind if you remove the stamp. I guess you would just have to cut them out and mount the piece of envelope in your album?