The URLClassloader getURLs call is returning URLs that contain %20 instead of spaces. The current code calls .getPath, which leaves the %20 in there and ultimately can't find the directory. Changing the .getPath call to .toURI calls a different java.io.File constructor and fixed the problem for me.
Applied in commit 8f116ba8c6944acc347cba97db0244e247021016
Mark old resolved issues as 'closed'