Using a named parameter in multiple places doesn't work

The following won't work:

$qb->andWhere('(a.campaign IS NOT NULL AND (cmp.user IS NULL OR cmp.user = :currentUser) OR a.previewTarget IS NOT NULL AND pt.user = :currentUser)')
   ->setParameter('currentUser', $currentUser);

The following will, but seems needlessly complex:

$qb->andWhere('(a.campaign IS NOT NULL AND (cmp.user IS NULL OR cmp.user = :currentUserA) OR a.previewTarget IS NOT NULL AND pt.user = :currentUserB)')
   ->setParameter('currentUserA', $currentUser)
   ->setParameter('currentUserB', $currentUser);

I would expect a named parameter to behave like a constant. I should be able to define it once, and then use it multiple times.

Also, I would like to be able to set the same parameter multiple times, so if multiple pieces of code set :currentUser that isn't a problem, unless they're different (in which case I'd expect an error like ":currentUser bound to two different values").