Designer not refreshing layout margins, eg. set 50 for top and bottom 50, then back to 0 and 0 for preview is ok (ctr+R), but on deisgner we still have 50 and 50. Save/close open .ui file again this same.

Also ctr+z etc. not helping, due this widget can overide others, eg. layout is over dock and going for another, event ctr+r is ok.