Same listen port with more than one WLS 8.1 manag. instance

Hello, again :-)
we've got two WLS 8.1 cluster composed by four nodes each one. For each cluster we have four WLS 8.1 instance that are configured with same port and different IP address.

For example:

ClusterA (as middle tier: ejb):
WLS1_IP1_7280
WLS2_IP2_7280
WLS3_IP3_7280
WLS4_IP4_7280

ClusterB (as front-end: webapps):
WLS1_IP1_7282
WLS2_IP2_7282
WLS3_IP3_7282
WLS4_IP4_7282

In Application Manager, we tried to add a new monitor on WLS1_IP1_7282.
In Application Manager console we noticed that in the "Monitor Information" for that server we had the same "Listen port" (7280 instead 7282) to the WLS1_IP1_7280.
That kind of problem caused the incorrect information to be displayed. In fact, we got the "EJB Details" and we didn't get the "Web Application Details".

Thanks in advance.

bye Stefano.