rebuilding of makefiles vs. headers

[Dan Manthey]

One of the last steps that ./config.status does when making config.h is to
check whether the newly generated file differs from that being replaced,
and if it does not, the old one is not overwritten.  This is done to
reduce unnessary rebuilding of source dependented on config.h.  This I
understand.

But the similar check for non-modification of generated makefiles is
commented out in status.m4.  Why is this?  There's a crypic "This would
break Makefile dependencies." in the comment, but I don't understand how.
Could someone enlighten me?

-Dan