I experienced something similar. The butt seam tape pulled off like masking tape on a couple of joints long after I had wired and glued the panels. From the discussion on this thread and my limited experience, I'd guess it to be caused by epoxy starvation. Perhaps related to the weight used. I used the mylar, covered by a flat piece of melamine covered MDF with a gallon jug of water ~8 lbs. I did not pre-sand or epoxy coat the plywood. My solution was to insure sufficient structure on the inside and glass the deck per instructions.

Next time S & G will be splined.

Greg

: on my first pigmy I did not like the light colored strips where the butt
: joints were epoxyied together. someone else mentioned this and they had
: talked to pigmy about this issue, and they decided to sand off the tape
: and epoxy before glassing the outside of the boat.
: So when it came time to remove the tape I thought that I would need to sand
: through the whole thing down to the wood to get it gone. but when I
: started to remove the tape, I was able to pull it off of the wood easely.
: I have had to remove more difficult duct tape. The epoxy remained on the
: boat, but the tape pulled off of the epoxy like it had not bonded
: properly.

: The question is, should I plan on sanding off all of the tape on the deck and
: the inside of the hull. If the tape is preventing a good bond with the
: epoxy, will it then act as a barrier for the rest fo teh fiberglass,
: causing a weak spot right on the joint when the rest of the boat is
: glassed in?