2011-01-26 14:14 AEST by Arthur Barrett - See bug report:
https://savannah.nongnu.org/bugs/?func=detailitem&item_id=14840

Also notes from user:


After a production cvs server was updated from Mandriva Corporate Server 4.0 
to Mandriva Enterprise Server 5.1, the CVS server version bumped up from 
1.11.x to 1.12.13.

  Concurrent Versions System (CVS) 1.12.13 (client/server)

After this update, a cvs client that is quite heavily used on Windows systems 
started to hang on various operations.  (Apparently a number of different cvs 
clients are affected.) 

Before the root cause was found, it seemed possible to log on to the server 
and look to see if the user's cvs process was still using CPU time.  Upon 
confirming that their appeared to be no client/server communication going on, 
using ^C on the client seemed to leave the CVS sandbox intact.

At first it seemed the problem mostly occurred when large files were involved, 
but it is not clear that large files have to be involved for this to happen. 
Eventually a bit of web searching lead to a WANdisco publication that led to

  bug #14840: zlib.c implementation in 1.12.12+ still broken
  https://savannah.nongnu.org/bugs/?func=detailitem&item_id=14840

It appears that the bug is server-side rather than client-side.  It was fixed 
in 2005, and a fix will ship if/when 1.12.14 is released.  Until then, it 
seems the options for avoiding the issue include reverting the server to one 
older than 1.12.12, or by building a new/patched one.