WebSphere MQ Adapter connections cannot be disabled

If we try to disable an MQ connection in the IS Administrator GUI, the connections remains etsablished.

IS 8.2.1.0 , IS_8.2_SP1_Core_Fix2, TNS_8.2_SP1_Fix2
MQ MQS_6.5_Fix14

IS is part of an IS cluster, disabling is not possible either if second IS is running or stopped.
From MQ same queue manager is used with two queues, one for inpiut , another one for output.

An application was deployed, but configuration of MQ is not possible.

Currently we “disable” the connection by adding firewall rule for reject connection to MQ (running on another host)

Does anybody has an idea what can be the reason for not disabling the connection?
and is a solution known?

Thanks in advance
Frank-Juergen Greger