It's a 32-bit-access-only heap. On the Ultimate Doom WAD the amount of
data moved is about 17 kiB, which is not a lot, but arrays with 4-byte
elements are not easy to find in Doom.
This occurs if all texture IDs on a particular line are multiples of
256 (like STARGR2 = 256) since the cast to boolean (byte) destroys
significant bits.