[PS 8] Irregular VAT display and gross prices are not saved

[Ritter]

Precondition: German provider and German IP, tax rule Germany VAT. 19%, only this tax, VATChecker modules installed, shop country: Germany, cache cleared several times.
The item price is 8.50 € gross with the German tax rule of 19% VAT. This is how it is entered and saved, but the following is displayed:

It gets even better if you temporarily change the tax rule. The 8.50 € actually appear for a short time, but after saving the price jumps back again ... I'm at a loss!

Animated GIF

 

Prestashop probably only works with net prices and calculates the net price when entering the gross price based on the shop location and only writes this to the database.
This recalculation does not work, the gross price is only displayed correctly if the correct net price is entered.

Edited December 8, 2022 by Ritter (see edit history)