Here's the best scenario I can think of at the moment. I'm hand-flying at low altitude in the holding stack and there's a severe, momentary up-gust, causing a momentary (rapid) rise in AoA towards alpha-prot.
Phase-advanced alpha-protection puts the FBW into AoA Protection Law. Meanwhile, the AoA has returned (fallen) to what it was before the gust. However, FBW uses up-elevator to increase the AoA to alpha-prot. The a/c climbs suddenly until I push the stick forward more than half-travel, OR use less-than-half forward stick for more than a second.
Although I'm unlikely to allow the a/c to climb much (unless I'm having a bad day at the office, or get distracted), maintaining AoA Law seems an unnecessary presumption by the FBW.
So my question remains: why does it not revert to Normal Law once the AoA falls to a safe value?
Hang on a minute! Suppose it is an A320 at say 60 tonnes - holding at 200 kts?
That will be about 5.5 deg AoA with stall at 12 deg. The alphaprotect logic is a combination of alpha and rate of change of alpha, but take just alpha for the moment. You are going to need a gust of 38 fps to get to the stall and from published A320 flight statistics you will need to fly half a million flight hours at 200 kts before you hit that sort of gust. OK one needs to back off a bit to account for the phase advance contribution, but it will still be a helluva lot of hours
So in theory you may be right about the possibility but it would be an extremely rare case I think.
As for why it doesn't revert to normal law, surely it cannot, because once alphaprotect has taken charge the AOA is held at the alphaprotect value?