The Scott and the pack howitzers are not following turn orders.
Turn doesn’t cancel another order that’s in progress. If you order a vehicle to move to a waypoint and issue a turn order before the waypoint is reached then the vehicle just keeps moving instead of stopping and turning.
Likewise, turn cannot be added to a queue.
Finally, the left panel shows multiple turn buttons if several different units with turn are in the current selection. For example, if you select a Stuart, a Greyhound and a halftrack then the left panel would display three turn buttons. All three units in the preceding example would follow a turn order regardless of which of the three turn buttons you used to issue the order.
I was testing svn rev 2091.