Netflix not sending DVDs reliably

Netflix has been really annoying lately.  On the surface, they're
being useful -- sending us DVDs before we've sent back the old DVDs.
But in practice, we're sometimes not getting DVDs we're supposed to
get.

The problem is that we have multiple DVD queues, one for items that my
wife Catie picks, one for items that I pick.  We have one DVD
allocated to Catie's list, and two to mine, since we both watch
through mine a lot faster.  Catie sometimes doesn't watch her DVDs for
a while.  When Netflix sends extra DVDs to one queue, they sometimes
don't send DVDs to the other queue until the extras are sent back.  So
if Catie has an extra DVD on her queue and doesn't watch it, then I
might not get one of my DVDs.  And if she has two extras, then I can
stop getting DVDs altogether.  This isn't how the DVD allocations are
supposed to work.  It's infuriating.

I've contacted netflix a couple of times to complain about this, but
the customer service folks don't have the ability to do anything about
it.  Very frustrating.