Monitoring additional SQL instances

I have an issue when I create a new SQL instance, on a server that already has one (or more) installed.

We have a rule which associates MSSQL monitors when it finds sqlservr.exe running. This works, and we get the MSSQL Dashboard View and MSSQL monitors.

The problem comes when we install another instance later - no matter how many times we re-run the rule, it will not associate the new instance with the monitors. However if we delete the monitoring for all existing SQL instances, then run the rule, it correctly associates all monitors/instances.

What I would expect the software to do is associate any new instances it finds, regardless of how many it already knows about.

Is this a known bug, or am I missing something obvious?

thanks