Cannot swap unit hexes condition

[eskuche]

When one unit can move only their one allotted hex but wouldn't otherwise have the OP to do it (out of supply unit, unit attacked already, too much terrain penalty + ZOC, etc.), it can't switch places with a second unit in the destination hex even though both units could make the individual moves.

[AlvaroSousa]

Probably due to ZoC. One is leaving ZoC, the other is entering.