When the towers have an alliance member who needs troops, and the tower has troops and is not on a timeout, but the stronghold has no troops, we are unable to assign troops from the tower to the member.
I have tested this several times, and it appears that there is a coding error or possibly a variable/flag for the stronghold troops that none can be assigned when stronghold troops are zero. Even when they are not coming from the stronghold, as in this example.
Additional: It appears that the troop assignment timer for towers is not functioning as was intended.
The timer is to prevent troop assignments until some time has passed, this appears to only be true for a single general/leader. I have been able to assign troops to a tower that another general has just assigned troops to, even though the timer has not completed running. So, if an alliance has a lot of generals, they have an unfair exploit to re-troop their towers at the front lines as long as they have troops to assign at their stronghold.