How to track down rogue persistence values?

Here's a trimmed-down version of my iRule. The `persist none` parts were the only change I made to fix the weird behavior.

 
 when CLIENT_ACCEPTED { 
   set lastPersist "" 
 } 
  
 when HTTP_REQUEST { 
    Some semi-complicated logic runs to set this, but isn't relevant to the 
    issue.  This will either set a real persistence value or one of the 
    constants used by the switch statement later. 
   set persistVal "" 
  
    Browsers tend to reuse connections when they can.  Webservers see each 
    request as separate, but the load balancer works on connections, not 
    requests.  Since the requests in the same connection may not share the 
    same perrsistence data we need to do an LB::detach to cause the request to 
    be routed properly.   
   if { $lastPersist != "" and $persistVal != $lastPersist } { 
     LB::detach 
   } 
  
   set lastPersist $persistVal 
  
    We only want to set persistence when there is persistence data in the 
    request. Static requests don't need any persistence.  We still set the 
    lastPersist value though so that we can detect when the persistence value 
    has changed. 
   switch -- $persistVal { 
     "STATICREQ" { 
        Don't set any persistence for the request 
       persist none 
     } 
     "NOPERSIST" { 
        Don't set any persistence for the request 
       persist none 
     } 
     default { 
       log local0. "HTTP setting persist to: $persistVal" 
       persist uie $persistVal 
     } 
   } 
 } 
 

I think the issue is related to the LB::detach. I'm guessing when the detach happens the string that stores the old persistence value is freed, but if no new one is provided by the iRule (the old behavior) it tries re-using it. Since it has been freed the string is now invalid, and so you get whatever happens to be in memory at that location.