Incorrect Discount

Here's my scenario:

I've created a coupon that applies to four of my manufacturers. Now here's what happens:

1. If I buy a product from one of the non-discounted manufacturers - it works fine, there is no discount.
2. If I buy one or more products which are from the discounted manufacturers it also works fine, the discount is correct.
3. If I buy a mix of products from discounted and non-discounted manufacturers then all products are incorrectly discounted (i.e. even the ones from manufacturers which were not included in the coupon).

I was running on version 1.2.3 pro and just upgraded to 1.4.0 but the issue still persists.

Please advice.

Thanks,

Johan

set the discount type to specific when setting up the coupon