1) Observe bad behavior.
2) Ponder long and hard about what might be causing such bad behavior.
3) Develop a theory and examine the code involved.
4) Discover comment explaining bad behavior and smack head with palm.
While it's gratifying to see my theory proven, it'd be a tad more useful if this knowledge were contained in some more useful fashion... or if, for example, the code LOGGED AN ERROR when the unimplemented case got hit.