Discount calculcation bug in 1.9.0.1

Question

I upgraded recently from 1.7 to 1.9.0.1 and I am wondering if this is a bug or if I just missed some new configuration, I am not using tax classes btw.

When creating a shopping cart price rule, (e.g. coupon, sub total equals or greater than 100, fixed discount for the whole cart 15), the discount applied on the subtotal diminishes with every additional product added if and only when setting "Stop further rules processing" to "Yes".

I tested this on a vanilla installation.