As far as I know, Debian armhf is compiled for ARMv7. This means that the compiled executables will sometimes use instructions that aren't implemented on older ARM cores. As the processor on RaspberryPi is ARMv6, don't expect to ever run the official Debian armhf. I think it is theoretically possible to compile for ARMv6 using hardfp, but at this point it seems unlikely distributions would put in the effort to improve FP performance on such old hardware.
I understand that now, but when you pull the trigger on dist-upgrade without that knowledge, you're going to want to revert it, and I needed to learn to read strace to figure it out.
I have put semi-instructions to go back in this thread, in case you want to try a foolish thing like I did.
