Simple to reproduce.

1- Create a stack of units.

2- Move the stack.

3- Only the top unit will have their remaining movement units reduced.

The only time group movement appears to apply correctly is if a group is breaking from a larger group.  Even then, it seems to only apply correctly on the first move.

**NOTE** All of this movement is done of the first turn.

Staring position:

Move two units:

Second unit still has 2 remaining move units

Third unit still has 2 remaining move units

Moving 2 sentinels off of General as a new stack, both now have 1 movement remaining.

Move 2 sentinels one more square.  The top sentinel has 0.0 movement left

The second sentinel has 1.0 movement left

Move the bottom sentinel 1 unit.  All units now have 0.0 movement left.