I think I figured out that precompile.pike takes a --base parameter, common_module_makefile.in uses it with $(MODNAME) as the value, and it's been this way for ages. In the source release tarballs, all files have the same timestamp, and what seems to have happened is that suddenly, make remakes targets with the same timestamp as their prerequisites. Or maybe one of the $(PMOD_TARGETS) somehow are older. The question now is why there seem to be several files in the source distribution generated with precompile.pike *without* --base.