I'm confused: you said "car stalls only when half full." Literally meaning, it runs fine with more fuel, or less fuel--it only acts up at precisely 1/2 tank.
Assuming you meant "car stalls only when half full or less," that, plus the fact that it stalls when decelerating, makes me think that the fuel sock, fuel baffle, or whatever means Honda uses to mitigate fuel sloshing is acting up.
This would explain a problem that starts around 1/2 tank (and gets worse as the tank is continually drawn down), but it doesn't explain a problem that happens ONLY at 1/2 (not at 3/4 or 1/4 or 1/8).
1. Did you mean (a)"only at half tank," OR (b) "only at half tank (or less)"?
2. If you continue to drive below 1/2 tank, does the problem get worse?
3. In addition to occurring when decelerating, does the problem occur when making extended turns (such as a "cloverleaf" on- or off-ramp)?