Hi,
It seems the code for the comparison of the basePriceWithTax and salesPrice is not working properly in some cases. The line I found in default.php for the category (if (round($product->prices['basePriceWithTax'],$this->currency->_priceConfig['salesPrice'][1]) != $product->prices['salesPrice'])) seems to be ok, but when the option 'Round only display' is checked in Virtuemart configuration, the baseprice is always displayed (as strikethrough). It seems a rounding issue to me, because I've now unchecked the Round only display option, which solves the issue.
Regards,
Richard.