The first title of the FWWC series France 14 was released with the same disruption movement rules as PzC, but in a post release update that was changed to allow disrupted units to retain their full MP allowance on day moves and revert to the PzC 2/3 MP allowance on night moves, here is the detail..............
Disrupted unit movement allowance change
This change was made to encourage players to retreat from unsustainable positions rather than hang on to allow disrupted units to escape to the rear and often suffer an even worse loss of units cut off and destroyed. To stop players taking advantage of the change to be able to push disrupted units forward an additional terrain cost in MPs to move towards known/spotted enemy units was imposed, (in practise most units will only be able to move a single hex).
1) During DAY turns, disrupted units now have full Movement Points (instead of 2/3rds under the original system)
2) During NIGHT turns, disrupted units have 2/3 Movement Points (no change)
3) During DAY or NIGHT turns, disrupted units expend 3x terrain cost in MPs to move towards known/spotted enemy units (of course a unit will always be allowed to move one hex, as per standard movement rules)
In another slight tweak to disrupted unit movement when a good order unit is adjacent to an enemy, and that unit is disrupted by defensive fire during the current turn, its remaining MPs are reduced by 1/2. This keeps units from moving up, getting disrupted and being able to speed away at full speed (or being able to fire twice).
I will allow Ed to give the reasons for this change from the designers POV.