Well, that was fun... not.
A few nights ago night there was a sharp crack! as the gum tape separated itself from the stretching board. Very spectacular. Never underestimate the tension that stretched paper can create! It was a very good reminder of why you need a rigid board. Not sure why the tape gave way. Maybe too much or too little water and the weather has been extremely dry here recently.
The sad thing was the painting was ruined anyway. Unsightly blotches had appeared on a particularly stubborn wash of paynes grey. The grey was from my Sennelier range (they are very high staining) and combined with the this particular paper made it impossible to fix short of sanding, a legitimate technique that wouldn't work in this case. I was stumped how they happened until I started the next version. I had simply tapped the paper a little hard when dabbing it with a sponge. That slight impact was enough to change the surface and affect the wash.