We have recently set to true the appconfig parameter: FreeShippingAllowsRateSelection
This allows us to set Freeshipping threshold prices while allowing prospective customers to choose faster shipping methods if necessary. Unfortunately if we switch from threshold prices to a coupon method for free shipping then the Order Total tends to add the shipping price even though it shouldn't.
Below are a couple of examples from the Orders table. The first row is when the above parameter is set to false and the second row is when it is set to true. We have set ShippingMethodIDIfFreeShippingIsOn to 1. Note: both orders below have CouponIncludesFreeShipping
ShippingMethodID OrderSubTotal Tax OrderShippingCosts OrderTotal
0 179.00 0.00 0.00 179.00
1 395.00 0.00 28.95 423.95
Below are some screenshots illustrating the issue at the checkout process when FreeShippingAllowsRateSelection is set to true.