A url like '/this+is+a+test' in the front matter ends up as /thisisatest in .Permalink, but the page is generated in the right spot which makes any link(s) in the rest of the site to that page unclickable.

The + sign is a legal character in a url and should be preserved wherever it is used.

update: it seems this also goes for the % sign (which I thought I might use as a work-around by encoding the + sign...).