"strip_path" is not work

Now i am developing a plugin to change upstream url with regex,
Then i found that after i set upstream url by " ngx.var.upstream_uri" or " kong.service.request.set_path", the new path will not be stripped by kong.

For example, if i have a route with path “/api/x-service” and checked “strip_path”, and request path is “/api/x-service/g-test-route/products”, my plugin changed the upstream url to “/api/x-service/products”, then kong will not strip upstream url to “/products” but still access “/api/x-service/products”, why? I hope kong could strip it.

Any idea is appreciated.