I played around with it and sadly I cannot reproduce this. I cannot tell where the issue comes from, but to me it would look like a configuration error somehow, because it doesnt matter if it is a Service Set or a Template, Apply Rule or a directly assigned service.
Select the previously created service template windows-disk , define the name as disk C: and use the custom property disk_win_path to assign the value C: to it.
Repeat that for the second service set with D: and E: services