Why does my mold do this?

[lenarenee]

I like the idea of trying something sticky to hold the liner to the wood. If you decide to try freezer paper, could you cut one or two pieces of cardboard the length and height of the mold (false sides) to put between the wood and the freezer paper in order to reduce the width of the mold?

That's a good idea - we have plenty of cardboard around here.