It seems that with GHC 6.2, -keep-hc-files and --make conflict: GHC deletes the HC files it makes. I found an old bug report about this, with a note from one of the developers claiming to have fixed this, but at least here the bug is reproduceable (a regression, perhaps?).

This is on up-to-date Debian unstable.

Looks like a bug; thanks for the report. It'll be fixed in the next release. Cheers, Simon