Yeah, it's not some native function of composite, apparently. It does some sort of sensing to select between composite or component. If you've got just the green jack used it changes to composite mode, if you've got all three jacks used it switches to component. In the TV's input selector they even show up as separate channels, it's got AV 1 & 2 and Component 1 & 2, even though there are only two sets of those inputs.
It's kind of a pain how it means taking up a component slot to use composite, but fortunately I don't have many component devices. Mainly the Wii for now.