Well, this is embarrassing. I thought I had done everything to avoid portability problems. But in trying to avoid them, I stepped right into them, doing something that by now I know very well not to do. Oh well, here’s an updated version of dmsetup-tc (which you can use to mount TrueCrypt®-encrypted Windows system drives/partitions on Linux). It’s no longer really necessary since the Linux version of TrueCrypt® added support for this back in version 6.0, but dmsetup-tc is still a lot more lightweight than that, so you might still be interested in it.
Download source code: dmsetup-tc-0.4.tar.bz2 (21 KB, updated 19th February 2012)
Some credit goes to oli of l33tbox.de for bringing the issue to my attention.
Update: the latest version, 0.4, now also fixes a problem with approximately 50% of encrypted partitions… but apparently exactly those 50% that never complained. ;)