Ian,
As David said this change was tested over a long period while we were developing a new FWWC title, so we can say for sure there are no issues associated with the rule change, it was also noted that clever players might actually exploit this change to move their disrupted units forward, so the change also has designed to prevent that unintended use.
There is no longer any reason for players to lose disrupted units because they are overtaken and trapped due to their reduced movement allowances (under the old system), if retreated promptly their survival chances should improve markedly.
I believe that broken units move full allowance day and night (will check that next game I play).
I listed the changes to the disruption movement mechanics in my "Evolution of the FWWC series" article and I have copied/pasted the relevant section below...........
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 greater 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 forward).
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 unit in good order 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).