connection to Informix still active despite closing?
Check your connection pooling (settings in IBM Data Server Provider).
I never used it, but the docs on IBM Data provider say:


  When a connection is first opened against a database, a connection pool is created. As connections are closed, they enter the pool, ready to be reused within the same process by other applications that need connections.


So even if you close the "session" from you app to Informix DB, a connection is still active between IBM Server Provider and the Informix instance.

Hope this helps.