If the enemy initiates a combat and you use escape, your army should have its full movement points when it becomes your turn. If this is not happening, try a fresh install. Or perhaps you really have found a bug. Try posting your save file.

As far as I know, any time the army leader is immobilised during combat, the entire army will have 0 movement after the battle.  This includes Webbing by spiders.

What the OP is referring to is that between Player turns you are attacked and then retreat and when it is once again your turn you have 0 strategic movement.  I had had this happen many time before and thought it was as intended and never thought of it otherwise but now that I do it might be a bug.

Actually, to add to this, when you have a move queued for the army that uses "escape", they will move their movement points automatically once escaping. So if you think you're going to get attacked when you hit turn, then just queue the movement up for when you use escape so they move where you want after and the 0 movement left doesn't matter. Annoying, but it works.

You may be correct, but have you consider using the escape trait in combination with a recall scroll (even though you have no movement, you may still cast magic)

There are other spells that will also teleport your army to another location and can be used after the escape from the battlefield.

The intent was to not allow the battles to be escapable, but since you may escape, you can reinforce your units if you have another unit nearby, thus, not making the escape useless, but a tactical decision.

The escape may not allow you to move your army away, but it can give you time to prepare your troops for another round. Say this particular army has fire attacks a plenty and you don't have any resistance on the particular army you brought to the battle. Hence, you can natures cloak to give you that resistance to help with round 2. Also, regen would heal you units to full health next turn. This may take a lot of mana, but it is a plausible strategy and not a completely useless action.