How build dependencies work/are supposed to work in 2.5

Quoted 3 lines · Petr Vandrovec

So I'd like to ask whether current kernel build system is supposed
to track changes in include files automagically, or whether I'm supposed to run 'make dep' from time to time?

Until now I'm only aware of one set of problems that kbuild does not handle correct. That is when the timestamp of the files goes backward. This happens at least in the following situations:
1) A file is saved, and mv is used to restore the original
2) CVS is configured to preserve original timestamp when files are 'dumped'
3) NFS mounted filesystems where the clock is wrong. Timezone inconsistency for eaxmple.

I assume you were hit by some flavour of 1) ???