In the last couple of week I've been trying to play several of my
Umbra/Penumbra Collection CDrs. Specifically those in 18x14cm plastic
wallets with art, the disc in another sleeve, sometimes with leaves and
shells. "Special packaging" Gigi calls it. The first half plays fine but after
half anhour the music is distorted with a periodic glitch. While some of you
might appreciate the industrial ambient generated, it rather ruined the likes
of
Floating on
Night Currents for me.

The disc looks fine. However,
placing it on a flat surface revealed that disc is concave (label upright).
They had been stored vertically but closely packed. So this is a word of
warning. Has anyone else experienced this sagging? How do other
Oophoifans keep their CDrs?
Can flatness be restored, say by placing discs horizontal between lots of heavy
textbooks for an extended period?