Dear Ed,
thank you very much for all the efforts!
I have installed the files you gave me. For normal products it works now. Not so for subscriptions though. It seems only to go wrong when normal products and a subscription are together in the cart. I use woocommerce subscriptions and since a recent version it is possible to purchase subscriptions together with normal products in one cart.
If this is a general compatibility issue which you cannot fix (at all or any time soon), please drop me a line and I will get rid of the cart in the top bar altogether. Would be sad though because its really nice. Or is there a hook/filter to get rid only of the sum and count? .
Thank you again and have a nice day!
Florian