I think you are running into a similar issue that I’m facing (Bug: Request URI mutation when saving). I’ve resorted to saving the request and then copying over all the parameters into a new ‘unsaved’ request when I need to use it.
I’ve been playing around with the pre-request scripts a bit and I think you might be able to resolve this issue by passing in the tail value (test) as a string stored in a variable by the prerequest script.