Yes this only works on $ off when you can select if the coupon applies to all products or first one only, % off sets this value to apply to first coupon only
Default XC code for product for example
Code:
if ($how_to_apply_p != 'N')
$how_to_apply_p = 'Y'; // Apply discount once per order
When you select % discount $how_to_apply_p variable has no value so its value is set to "Y". So QT decided that if you want % off this should be applied to first product only no matter what. Of course this can be changed in the code but I didn't change the default XC behaviour on this - my mod just follows it