Hi guys,
I found a solution that works for me.
At least the only thing I've done was to deactivate a setting in price settings.
Actually I have no idea what it is, but I don't need it.
After deactivating it, the crossed price (which is same as the normal price) disappears.
So the crossed price will be only shown for real discounts (before for e.g.).
Screenshot is in german, but you will find it I'm sure.
Configuration --> configuration --> Price settings
[attachment cleanup by admin]