xdg-open doesn't expand %u in Exec if it's not delimited with spaces

Consider the following desktop entry:

[Desktop Entry]
Exec=seamonkey -remote openURL(%u%,new-tab)

Here, %u is never expanded upon execution, and the actual command executed is

/usr/bin/seamonkey -remote 'openURL(%u,new-window)' http://example.com

Your documentation doesn't mention that such a limitation exists.