In making a backup copy of a site I'm involved in (we're changing webmasters, and the site may also be moved to another host), I've noticed that requesting resources with spaces in the name returns INVALID REQUEST. (The site is essentially a static site, and for testing the copy I've temporarily stuck it in a subdirectory under the static folder of one my apps.) The html has the spaces already escaped (%20), which works on the current primary host.
This is 2.16.1 running on Ubuntu 16.04 with gunicorn as the front end. Looks like the Python version is 2.7.12.
Dave S
/dps