I don't think multiple heights for fields are even possible. It's just that in p128, a rectangle of 128x64 px is marked as dirty, rather than the full 128x128 px square. In p192c, it's 192x96px rather than 192x192px.
Since it occurs so rarely, not via 'normal' gameplay, and is fixed so easily by moving the map, it probably has the lowest possible priority to fix it.