It appears we've already sorted this out with you via email, but in case anyone else reading this may have a similar problem, here was our response:
Please see the section on Combining Discounts at the bottom of our help page here for an explanation of when discounts can be added to each other:
If a discount has no Discount Code entered and it is set to apply to "all cart items", it will always apply automatically on every order, at least until its Max Use Count limit is reached. If you want to require that a code be entered for that discount to be claimed you will need to enter a code for it, but bear in mind that a buyer could still enter that code in addition to the code for a product discount and receive both.
If you are giving away $100 product discounts and you also have a 25% order discount those will both apply at the same time. There is no way to prevent this at all because those are two different types of discounts which are allowed to stack, and we cannot change that behavior since everyone else has created their discounts with these settings in mind.
I'd recommend removing the 25% discount, or perhaps lowering the amount of the product discounts so that they can work alongside the 25% discount without reducing the order total too much.