How to determine last segment in reaseembled TCP packet

I've got the following problem with my iRule when a client uses multiple threads using the same source port for all the threads.

Doing a TCPDump I can see the transactions coming in on the outside interface, on the inside interface it goes the the nodes and I can see the response returned from the nodes. But I don't see the response leaving the outside interface. The result is that the client don't get the response and eventually times out.

iRule:

 
 when RULE_INIT { 
  set ::eot "Marker" 
  set ::eot_found 0 
 } 
  
 when SERVER_CONNECTED { 
  TCP::collect 
 } 
  
 when SERVER_DATA { 
  set payload [TCP::payload] 
  
  log -noname local0. "iRule: Request from [IP::client_addr]:[TCP::client_port] load balanced to [LB::server addr]" 
  
  if { $payload ends_with $::eot } { 
   set ::eot_found 1 
  } 
  
  TCP::release 
  TCP::collect 
  TCP::notify response 
 } 
  
 when USER_RESPONSE { 
  if { $::eot_found eq 1 } { 
   set ::eot_found 0 
   LB::detach 
  } 
 } 
 

After adding the "log" to "SERVER_CONNECTED" event I get the following error in the log file. Without this line no errors were logged.

TCL error: - Error: No clientside connection established (line 6) invoked from within "IP::client_addr"

Why would doing a LB detach effect the client side connection ?

Thanks

Tiaan