Under IE 7, in the Order screen, if I bring up the Shipping dialogue box (by hovering the mouse over <<), and then pull down the "shipping via" combo, if I then hover the mouse over the entries in the pull-down list, the dialogue box vanishes after a short delay (around 0.5s). This means that you have to be quick in selecting an item from the combo before the dialogue box disappears.

I observe the same effect with the payment dialogue box, which has the "payment method" combo.

Under firefox I don't observe this effect and the dialogue box correctly remains on display until I move the mouse out of the box.