RPC-COUNTCALLS tests connecting to the [\pipe\rpcecho], presumably to test the RPC echo service.
Windows does not support the RPC echo service. It, or any Microsoft extension to it, or similar service, is not in the MCPP or WSPP documentation.
When the target is Windows, RPC-COUNTCALLS shouldn't bother trying the [\pipe\rpcecho] service even though its listed in ndr_table_list.
The RPC echo test is valid and intentional, in this 'discovery' test. This test is designed to discover how many calls all interfaces we know about supports.
rpcecho can be installed on Windows to test the behaviour of the Microsoft DCE/RPC stack. As such, I think it's best to thank you for your report, and mark this bug as INVALID.
It might be best to discuss your proposed testing strategy and findings on samba-technical, so we can understand better what you are trying to do, and how best to work with us on these issues.