i also think so (until now) .
I had also both Leos on same HD and had major problems. Even if added an boot-uuid diffenent in each /extra, chameleon loaded the things always from that volume which as actice for boot, even i selected (F8) the other volume.
I would simple copy each extensions from extra (whcih are differenr between SL +L) into his /S/L/Extensions folder (sure, with chown -R root:wheel for each) and delete each extensions.mkext in /extra.