Cool, that worked ... sort of. It came up at $11.89, then when I signed in, the price changed to $12.14. I'm not sure why. I'd like to update my first post, but I'm not sure which price to put. Any ideas on why the price changed when I signed in? I did this on a separate browser and account, btw.
A) $15.99 * 0.9 - $2.50 = $11.89
B) $15.99 - $2.50 * 0.9 = $12.14
"Order of operations" Should help you get option "A".
Only thing I can think of, is that you have "clipped" the coupon before, hence it was already in your account before the 10% off, resulting in option "B".
Hope this wasn't too confusing.