Storage options passed to unexpected backend

I'm looking into chaining caching with HTTP/S3 access as part of intake/intake_geopandas#15, and found some unexpected behavior with with chaining. My expectation of **storage_options was that each dict would be passed as kwargs to the relevant sub-filesystem. The problem I ran into is this: suppose I have a set of paths, some of which are intended to be cached and some of which are not. In that case, the HTTPFileSystem without caching was passed the caching options, and it passed those options as kwargs to requests, which failed:

import fsspec

path = "https://github.com/intake/filesystem_spec/raw/master/README.md"

# Succeeds
with fsspec.open("simplecache::" + path, simplecache={"cache_storage": "/tmp/testcache"}) as f:
    print(f.read())

# Fails as simplecache is passed to requests
with fsspec.open(path, simplecache={"cache_storage": "/tmp/testcache"}) as f:
    print(f.read())

I suppose I had expected storage options for filesystems not involved in a given path to be ignored. Is this behavior expected?

Reproduce the two fsspec.open examples, then trace how storage_options are routed through the simplecache and HTTPFileSystem backends. Check the option handling around requests and filesystem chaining; done means options for backends not used by a path are ignored without breaking the existing cached-path behavior.