Problem with partially added taxes when using the WooPrice Calculator

Hello guys and girls,

we are currently setting up a woocommerce shop for Switzerland. Switzerland currently is running with a tax of 7,7% percent. The base price of the products is already including the tax. Everything so far is working great except when we try to use the woocommerce Calculator. Prices are 7% percent to high. It seems the Calculator is trying to add another 7,7% percent to the already fixed price that is already including the tax. On top of that, the calculator is only adding the 7% and not 7,7% tax (maybe it has something to do with the Switzerland using the semicolon as decimal point? just a guess in my side).

Also, the problem occurs when working without a base price.

Screenshot 1 showing a product with a base price (including tax) 10,00.
Screenshot 2 showing another calculator, different formular, base price of 10,00 and with the same error.
Screenshot 3 showing a standard product without the calculator and a base price of 10 - the displayed price is correct.

Entering the prices without the taxes and adjusting the woocommerce settings didn't have any effect on the problem.
Also changing the the decimal point to semicolon and back didnt have any effect.

Any ideas on how to solve this problem?

thanks in advance,

Michael