Service connection calls doesn't work with filter criterion

Summary

Service connection calls doesn't work with filter criterion, but business object endpoints do

Content

I tried creating a select dropdown which has values dynamically assigned through an SDP. the SDP fetches record fro a BO calling its endpoint. The BO has more than 100 records and it just works fine. Search also worked fine in the select dropdown. The rest call goes wit the filter value.

Then I created a service connection for this BO and assigned the same service connection to the SDP with query parameter q. now when I search in the select, it doesn't shows up more the results.  Rest call goes for each key I type in but the filter/parameter isn't appended, because of which i am not getting the intended value.