1. Wave $09 (0000 1001) has the so called "test bit" set, and also the gate bit. I think this resets the phase and hangs the envelope until you unset bit 3, mostly used to produce a snappier and more consistent attack.
2. Only the upper nybble is used for waveform selection, so really the waveforms are 1*, 2*, 4*, 8* and so on (they can be combined since they are all on different bits in the upper nybble). The least significant bit (the one you see changing in the lower nybble) is the gate bit, which is used to trigger and release the envelope, much like a gate signal in an analog synthesizer would. Having it set lets the envelope go through the attack/decay cycles, stopping at the sustain amplitude. Unsetting it will trigger the release section of the envelope.