Coupon discount in no allowed dates.

Hi, this is the case:

1-I created a coupon valid only from september 01 to september 30.
2-I search in availability module to checkin september 16 and checkout september 18.
3-Apply the coupon and all the tariffs are ok.
4-Then I search to checkin october 01 and checkout octuber 03 and the tarrifs have the price with the discount of the coupon. WHY?
If the coupon is available only from september 01 to september 30, why the price of the room has the discount if the check in is in october or another date. I need to fix this to sell solidres to my client.

Thanks.