asterisk users - Jul 2005 - Ring requested on channel already in use?

We've had a recurring issue on one of our servers where one or more zap
channels from a PRI will get "stuck" causing incoming calls to fail. 
I
happened to have a CLI session when it happened this morning.  The start
of the problem looked like:

   -- Channel 0/3, span 1 got hangup
   -- Channel 0/3, span 1 got hangup
Jul 18 08:34:54 WARNING[20343]: chan_zap.c:7585 pri_dchannel: Ring
requested on channel 0/3 already in use on span 1.  Hanging up owner.
    -- B-channel 0/3 restarted on span 1
Jul 18 08:36:31 WARNING[20343]: chan_zap.c:7585 pri_dchannel: Ring
requested on channel 0/3 already in use on span 1.  Hanging up owner.
Jul 18 08:36:31 WARNING[20343]: chan_zap.c:7585 pri_dchannel: Ring
requested on channel 0/3 already in use on span 1.  Hanging up owner.

These messages (Ring requested...) then repeated until we killed and
restarted asterisk.

I don't normally see a channel get hungup twice in rapid succession.  Is
it possible that asterisk tried to deal with hanging up the channel from a
single call twice and left it in some stuck state?

Asterisk CVS-v1-0-07/05/05-10:54:39
zaptel and libpri were checked out/built/and reloaded when we upgraded to
this cvs snapshot of asterisk.  This system has 2 T100P cards, though only
one is in use.

----------------------------------------------------------------------
 Jon Lewis                   |  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
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