Try to open a file in qbittorrent and the filename will have %20 instead of spaces, which fails in xdg-open with a 'file doesn't exist' error.
A simple workaround is to do something like this:
url=`echo "$url" | sed 's/%20/\\ /g'`
But this will probably mess up internet urls.
I don't know how widespread the problem is or whether it's only a problem with qbittorrent, but I thought it was worth reporting it.