1.7.1.0 bug setting impact on unit price

[folkifoon]

I have a product with 2 combinations

One of the combinations has a lower unit price, so i set:

Impact on price per unit (tax excl):  -8,95

At this moment the two combinaitons have 0 quantity.

Now here is my bug, when i give bothe combinations a certain quantity (100) and i save this.

When i go back to the product catalog, and reopen this same product, the impact on price has been changed from 8,95 to 8.
This is only when i have the dutch language selected in backed, the english language doest seem to have this problem.

I made some screenshots to show the problem.

What can this be?
 

[folkifoon]

Can someone take a look at this problem or can i post it somewhere else?