Units movement differences

[Murphz]

Hi all,
I need a small info.

Sometimes happen that units have differences in movements and some units (often just one) stopped before the end.

Example: one HQ with 18 points movements and 3 units with 12 points movements, I click for a movement on a hex far 12 points from the group and, for some reasons, some units remain hexes away with 0 points movements.

What is strange is that some units reach the choosen hex and one not, why that? They start from the same hex and use the same path, so why this difference?

Thanks,
Murphz