Client losing connection with the F5

Yes, when you add the HTTP profile that enables processing in the BIGIP that tracks the state of HTTP requests and responses. The error message you are seeing indicates that the previous response was not finished according to the BIGIP. You should be able to reproduce it with the HTTP profile added, but without the iRule. I was just pointing this out because it seems the support department will often first refer people to DevCentral if they think it is an iRule problem.