Symptom:

VTY sessions timeout and go idle but do not clear entirely.  When in this state the VTY sessions will not clear.  

show tcp brief     provides a null output

show user           displays the idle sessions

show tcp vty <line#>    provides a null output

clear tcp tcb *      did not clear the sessions

clear line vty <line#>
[confirm] [OK]        did not clear the line as it still displayed in 'show user'


Conditions:

Normal operations.  Router was up over 30 weeks when the problem manifest.