Not allowed to move into hex with invisible unit?

[Liebchen]

I'm playing a game where either of two stacks of units could move into an adjacent hex. Terrain is suitable, ZOCs are not an (apparent) issue. The units all have their full movement allowances.

The game won't allow any of them to move into the hex because, "Cannon move into hex containing enemy units."

If there were hidden units there, I should see them, now that I'm adjacent to them. If they're blocking movement, I should be able to at least fire on them. But they're invisible - and apparently also impenetrable!

They can't move into a different empty hex because apparently the invisible unit is also exerting a ZOC that precludes ZOC-to-ZOC movement!

See the illustration. The woods hex next to the US infantry is apparently "occupied."



It won't even let me assault the hex!