Logout doenst seem to work

I open around 10 connection at the same time. After the job is done I logout them. Then open again 10 connections then logout then again 10 connections. Problem is that on 26th connection I got error. I guess is related to limitations of 25 concurrent connections per application. I`m sure that I never have over 10 active connections because I logout from them each time I go to next batch. What I`m doing wrong here?