Assign Catalog to Store; Show as Match greyed out

 Assign Catalog to Store; Show as Match greyed out
Hello,

I'm having a look at ORACLE eContent Manager, 11.510 environment.
When editing Stores, you can assign Catalogs.
When assigning Catalogs, you can tick a cherckbox called "Show as Match".
In some cases this checkbox appears to be greyed out for Catalogs already assigned.
Apparently in some cases you can't change the value of this checkbox.
We're after an explanation/overview of such cases.

KInd regards,

Rene Venema