You've probably encountered this bug yourself: a power's icon in your tray is full-sized and lit up, but you go to activate it and you get the "Recharging..." message. Maybe you get hit by some recharge-modifying effect and the client recalculates all your power recharge states, and the power greys out on its own to show it's still recharging. It happens when there's some kind of hiccup in the mapserver and the client gets ahead of where the server says your powers are. It seems to be happening a lot more on Homecoming than it did in the old days on Live.
Now, I don't know anything about making this stop happening entirely (though that would be ideal), but I think I have an idea to keep the bug from tripping us players up in combat. In the General Combat chat channel, every time a power recharges you get a message about it. "Hasten is recharged," for example. These messages come from the mapserver, and they aren't affected by the bug. If there was an option to only light up powers after use when this message is received from the server, the client should stop getting ahead of the mapserver when depicting power recharges. The General Combat messages are already being sent from the mapserver to the client, so this option wouldn't affect network traffic at all.