Why does Click Down state not stay?

I'm experiencing something rather weird with buttons. I have a movieclip with a few frames for the different button states. I have labels for _up _over and _down. I set buttonMode=true;

The button works but when I click and hold the mouse down, the down state only stays for about 1 second and then reverts to the _over state.

Is this a normal thing?
I am using CS4 and publishing to AIR 1.5

The reason was I had a

addEventListener(MouseEvent.MOUSE_DOWN, mouseDown);

defined for the main root and that seems to interfere.