Okay, nevermind, I found my typo...
CDEF:la=avg,100,/ accidentally got changed to cdef:la=avg,100,/
So the moral of the story is, the hobbitgraph.cfg (due to RRD) is case-sensitive. If a graph isn't working right, check the case, and you'll likely find your answer.
I've run into a very peculiar problem where the CPU (la) graphs are gone on
ALL of my hosts. The strange thing is, ALL of the other graphs for ALL of the hosts are still showing. Just the CPU graph is gone. This is for both the CPU column, and the trend page. The only thing I did was add a new server-side script, and two entries in hobbitgraph.cfg (and the graphs for this script are working fine too). There were a few bugs in the script which I have since fixed.
None of the hobbit logs I have looked in so far have given me any indication what is going on (though I may just not know exactly what it is I'm looking for). I checked the rrd files for all the hosts, and the cpu/la rrd file looks normal. Any ideas what log files/etc I could use to troubleshoot this?