Unable to Assign Common Routing for an alternate routing

We are on  12.2.3  and trying to assign a common routing to a part X with alternate designator A but when we navigate to the assign comon routing screen and enter the common routing part Y in the common item field , the field does not recognize the value Y though Y has a routing but not with the same alternate designator A - it seems you can only choose those common routings that have the routings for the same alternate designator as the part you  uare tyring to create the routing for so in the case above we can