A similar example is in wholesale production.

Here is a link that might be useful: Parthenocissus quinquefolia 'Monham' P.P.# 10128

Look like a Rubus of some sort.

I agree, it looks EXACTLY like some sort of rubus vine, although that's the end of my insight.

So would the white leaves reflect a genetic mixup of sorts (essentially a sport of some sort -- I know some really neat plants start that way, by an accident of genetics) or are there forms of Rubus that are almost white like this? It isn't even variegated ... It's almost pure white!