"Minimum purchase amount" of paypal payment method does not work if paypal is the only payment method

I tried to set up ecommerce for users to donate in order to be assigned to a specific role. As payment method, i want PAYPAL only.
I also want to have a minimum purchase amount.

Now i've tested the shopping cart and added as payment method "C.O.D." and "PAYPAL". With these two payment settings, "Minimum purchase amount" works fine, if a user tries to donate less than the minimum purchase amount and selects PAYPAL as purchase method, the user gets an error message "Your purchase total must be at least x.xx$".

But when i deactivated the "C.O.D" payment method so that only PAYPAL was left as payment method, the user who tries to donate less than the minimum purchase amount set in the paypal settings does NOT get this error message, the user can now purchase things cheaper than the minimum purchase amount. I think this migth be because if i only have PAYPAL as purchase method, it skips the "Payment Method"-Screen... If there are more than 1 Payment method, the error message is displayed correclty..

Is there a way to get "Minimum purchase amount" working if the only payment method is PAYPAL?
Thanks for your help!