First and I am guessing this is what is happening do you have Source persist enabled? This will push the request to the server in the source persist table before you ever see the request.
If you do not I did find this Dev central posting from 2009 that show the same issue
https://devcentral.f5.com/questions/-address-in-use-tcl-error
There they look for the [IP::server_addr] with a catch statement, if the catch statement fires then the request has not been load balanced if it has then you fire off a LB::detach and then use the pool command.