I've got a similar problem with Stray Random Quotes to this issue with Use Google Libraries:
http://wordpress.org/support/topic/297488
Basically, using WP_PLUGIN_URL seems to bypass all attempts to make admin URLs HTTPS. This gives users the unnerving "Do you want to display insecure items?" prompt - and these days IE seems to give the default response as "No".
My fix for now is using the code in the above post. For stray_quotes.php, change this line:
define("WP_STRAY_QUOTES_PATH", WP_PLUGIN_URL . "/" . STRAY_DIR);
To this:
define("WP_STRAY_QUOTES_PATH", plugins_url( "/" . STRAY_DIR ) );
Any chance of this making it into the next release? Thanks!
