drywallers around here are finding that they are having more cracks at window and door corners when they began using the fiberglass tape. Something about the fiberglass not moving and sticking as well or maybe too well. Many are switching back to paper. It could be the drywallers saved on drywall by leaving seams at the corners and patching in above the windows and doors instead of running full sheets over the opening so the seam is around the middle above the window or door. Repair may include cutting out the old tape and retaping and mudding.