No, I don't have an NVidia card. I've got an Intel integrated one.
I've found the reason. It's acpid_1.0.6-16_amd64. I downgraded to the version acpid_1.0.6-15_amd64. To do this I took the previous lenny package from the mirror
http://ftp.hk.debian.org/debian/pool/main/a/acpid/. Not every mirror has previous versions, so it seems I was lucky to get it.