Does shield drain work when your energys full ?

[Fatal]

does it still do damage to the enemy ?? :)

[xEik]

No, it deactivates as soon as your shield reaches 100%. However, sometimes it stops at 99% or some value near that.
That's what I would say from playing one player mode. The definitive answer would need trying two player mode and see what happens when a mate drains your shield. I guess you can try by yourself. ;) At the moment my PSX is hundreds of km away.

PRACTICE LEADS TO PERFECTION !

[Task]

You're absolutely right xEik, it has no effect whatsoever.