Trouble with ActionMaps

Hello,
I am having some issues with ActionMaps. The problem I am encountering is that when a modifier key is pressed (SHIFT, CTRL, ALT) and then another key is pressed, the down press of that key is detected, but the up is not. For example, with the following code:

moveMap.bindCmd(keyboard, "u", "toggleDown();", "toggleUp();");
function toggleDown(){
	echo("u Down");
}
function toggleUp(){
	echo("u Up");
}

I get the following:
<shift pressed>
<key u pressed>
"u Down"
<key u released>
nothing happens...
<key u pressed>
"u Down"


Am I doing something wrong here?

Thanks!