This has been reported upstream with a patch, though upstream seems to be dead: https://savannah.gnu.org/bugs/?32122 I've verified that this fixes the problem on my system.
Hum, just noticed the bug was already fixed upstream. Maybe the fix should be pulled from their CVS instead.
For references, that's: http://cvs.savannah.gnu.org/viewvc/texinfo/texinfo/makeinfo/sectioning.c?r1=1.30&r2=1.31&view=patch http://cvs.savannah.gnu.org/viewvc/texinfo/texinfo/makeinfo/sectioning.c?r1=1.31&r2=1.32&view=patch
most likely fixed with texinfo-5 due to the C->perl rewrite