How you configured promotion "Availability & Coupons" merchanising tab? I got some problem with coupon and remember that configuring "Requires customer action" option solved problem.
Can you try? Also, can you enable debug at CouponFormHandler and paste log here?
Hope it helps.
When you removed the coupon from Order summary page, have you executed the reprice order chain?
We need to execute the reprice order chain after removing the coupon/promotion from the order.
Hope this helps.