Isolated Units

[Compass Rose]

I am having a hard time understanding why one of my units (Red Square) is labeled as Isolated.

The unit was moved forward towards the enemy on turn one, into a hex that had a minefield in it, which ended up being adjacent to a enemy position.

At the beginning of turn two, it is shown being isolated even though enemy forces are adjacent on only one hex side while friendly forces are adjacent on three hex sides.

Can someone explain why this is?

Also, where in the manual does it talk about what causes a unit to become isolated?

The only thing I can locate is in the User Manual page 77 which only describes what happens to a unit once it is isolated.

Thanks