when you vote on nodes who are on the same page under each other, each vote gets assigned to the node on top.
eg:

node1,
node2,
node3

vote on node2 results in vote assigned to node 1
vote on node3 results in vote assigned to node 1
etc...

custom_vote_form_submit seems to be the problem,
it always takes the last node $form_values

if you are on a node page this is not a problem, but with several nodes on 1 page it is.