Hello,
Ok the steps that I took:
installed v1.8 updated it to v1.9.
in admin I set aan special item with a discount of 10%.
Then I made 2 customer groups 1 with a discount of 20% (named reseller) and 1 with no discount (named klant dutch for customer).
I made 2 customers 1 with the status reseller and 1 with klant.
I logged in with the klant account and everything works perfect.
Then I logout and login as reseller account and the normal products in the categories.
Then I went to the specials and I saw that the specials where not 10% but 30% discount.
This only happens by the reseller account.
I hoop that I informed you well enough.
greets