If log is made more topological, and uses contexts, then my patch to 
issue1327 should help for this.

Related: issue1839.  I recently complained on the mercurial-devel list about
this, and Matt sketched a possible solution.  See
http://mercurial.selenic.com/bts/msg11726.

Personally, I think this is a pretty embarrassing bug, since it's a
regression relative to CVS.  If there's one thing CVS knows how to do, it's
show the history of a single file.  Too bad Mercurial can't do it reliably.  ;-(

Won't fix.

When identical changes are made on separate branches, the manifest for the
second commit will reuse the filelog entry for the first.

When you then specify a file (instead of a pattern) for hg log, the second
changeset will incorrectly fail to appear in hg log output.  For the same file,
specified as a pattern, both changesets will appear correctly.

Example:

% hg log -l 4 --template '{rev}\t' usr/src/uts/intel/ip/ip.global-objs.debug64 ;
echo 
8037	8023	7749	7502	
%	hg log -l 4 --template '{rev}\t' -I
usr/src/uts/intel/ip/ip.global-objs.debug64 ; echo
8037	8032	8023	7749	
%	

This problem showed up in the same workspace as issue 1327, and (like 1327, I
believe) stems from reuse of identical filelog entries.