CLONE -Forcing language to en_us at course level breaks links to help files

0. Install English en_us package
1. Set default language to en_us for site
2. Force language to en_us at course level

Afterwards links to help files (via ? icon) are broken. Set Force language option to anything else (en or nothing) yields good links

A link when force language is set to en_us looks like this:
http://ourmoodlesite/moodle/help.php?module=moodle&file=search.html&forcelang=en_us_utf8
which reports "Help file "search.html" could not be found!" even though the link to the index of all help files in this window works fine.

The same link with force language set to en and nothing respectively, look like:
http://ourmoodlesite/moodle/help.php?module=moodle&file=search.html&forcelang=en_utf8
http://ourmoodlesite/moodle/help.php?module=moodle&file=search.html&forcelang=
both of these work.