I've found that contact receivers that are looking for a "Hand" contact have odd behavior. If you enter the contact with any part of your hand, it works as expected, but if a single finger gets removed from the contact, the contact will act as though the entire hand was removed from the contact, even if the rest of the hand is still present in the contact.

This was tested with a constant contact that drives a bool parameter.

This bug may lead to unusual effects with avatars that need a hand's constant presence, but the receiver isn't fixed onto the hand.