Consider the following:

package test15;
public enum MyEnum {
  A, B;
}

And:

package test15
class Test15 {
	void foo(String s, MyEnum e) {
		def d1, d2
		switch(e) {
			case MyEnum.A:
			 d1 = new Date()
			 d2 = new Date()
			 break
			case MyEnum.B:
			  d1 = null
			  d2 = null
			  break
		}
		foo(s, d1, d2)
	}

	void foo(String s, Date d1, Date d2) {
		
	}
}

Hit F3 over the call to foo(String, Date, Date) in foo(String, MyEnum) and/or look at the hover: Greclipse thinks that call is for foo(String, MyEnum) itself.
The cause of the problem seems to be d1 and d2 be declared as def together with the presence of the switch.
I think this case is a bit complicated to correctly analyse, but probably something can be done, because if you invoke Call Hierarchy (Ctrl+Alt+H) from foo(String, Date, Date), the call from foo(String, MyEnum) is correctly detected!