Hi,
The issue has been fixed. Actually it is not actually a fix but at least it eliminates the confusion. Basically when the "custom field" is "Generic Child Variant" type, then it doesn't show off in the category browse page. Unfortunately hiding that custom field from the configuration was the only way which works.Otherwise there were some Core editings were required, which would eventually create other problem in the Virtuemart Component updates.
I am emailing you the guide to apply the patch.
Cheers.