I've been banging up against this problem for awhile now where the admin starts having problems: javascript parse error on publish, navigation failing, perpetually spinning loading icons, the site tree padding growing vertically when trying to navigate, etc.
Interesting I have discovered that adding the following lines to mysite/_config.php "fixes" the problem:
Director::set_environment_type("dev");
Debug::send_errors_to('my@emailaddress.com')
I'm wondering if anyone knows what's really going on. I'm really just a front end guy.
Thanks in advance,
J