Right now, the number 6.50 which I want to save in the database will end that it will be saved as 6,50. The plugin will at the end return 6.00 again.
When I make a little hack:
wpsc-admin/includes/display-items-functions.php Line 138
<input type='text' class='text' size='10' name='meta[_wpsc_price]' value='<?php echo ( isset($product_data['meta']['_wpsc_price']) ) ? number_format( (float)str_replace(",",".",$product_data['meta']['_wpsc_price']), 2, '.', '' ) : '0.00'; ?>' />
then the str_replace will replace the Comma with the point and your function will work and show 6.50 also after several savings ;)
Have seen on other pages that you have this problem on price and also on taxes, which I didnt fix as I dont need it.