Function overloading is not working with Source Function feature

I am trying to migrate the UDF functions that we have in MetaMatrix 5.5.4 into EDS and found an issue with Function overloading is not working with Source Function feature. For example, we have GREATEST oracle source function with signature as shown below.

GREATEST (expr1 timestamp, expr2 timestamp) RETURN timestamp;
GREATEST (expr1 integer, expr2 integer) RETURN integer;

But designer throws an error "The name GREATEST is the same (ignoring case) as 1 other object(s) under the same parent" as shown in the attached screenshot.