Hi Scott. The first thing that comes to mind is that porcelain tile requires the use of a polymer-modified thinset. You can use the TEC medium bed mortar but make sure you use an acrylic latex additive at preferably 100% (no water).
Secondly, you cannot apply Redgard directly over gypcrete without using a primer. Here is a link to a Redgard PDF outlining exactly how to do just that.
www.custombuildingproduc... Redgard should not peel up easily as you described. In your case, the floor needed to be primed. Over standard concrete floors if this happens it is usually because of surface contaminates such as oil or dust.
Michael Prachniak - Expert Tile and Stone Consultant and Writer, Owner - Tile Productions
Check out FAF''s tile section!
www.findanyfloor.com/tile/TileFloo...