Confused white (cabbage) butterfly - on broad bean

For some reason we have lots of white butterflies on our broad beans - even though there is a row of cabbage plants right beside them! They flutter around all day, apparently chasing each other, maybe it's mating season, but they don't appear to be laying eggs.

The cabbages, broccoli, and cauliflowers all seem to be untouched. Long may it last!!

I found it hard to get texture in the wings and in fact the shots I thought were well under exposed were the best.