This article is from the SSH - Secure Shell FAQ, by Thomas Koenig Thomas.Koenig@ciw.uni-karlsruhe.de with numerous contributions by others.
This is due to a known race condition in the ssh protocol before
1.2.13.
Some changes have been made to the protocol in 1.2.14 to prevent this.
Unfortunately, these changes may also cause hangs when using TCP
forwarding between 1.2.14 and earlier versions. In these cases,
upgrade to 1.2.14 or later at both ends is recommended.
 
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