1. So high speed protection applies a nose-up pitch demand to control the speed. If you're at high weight / high level, this pitch up may be sufficient to trigger angle of attack protection. At this point the sidestick commands angle of attack directly, and acceleration will actually result in a climb. The only way out of AoA protection is a forward input on the sidestick, which if you're flying level will require a slight descent. This isn't ideal so I suppose that Airbus modified later ELACs to not do it.
2. Result of flight testing, I guess.