Use of backgroundURL in Configuration widget breaks OWF in IE 11

[ghost]

Summary

Setting the backgroundURL field in the Configuration Admin widget will break OWF in IE 11.

Steps to reproduce

1. Download a 7.17.1 GA bundle
2. Run the bundle
3. Login with the stock testAdmin1 account
4. Open the Admin App and select the Configuration page
5. Select the "Branding" option
6. Enter a path or URL in the backgroundURL field. Exit that field so the value is persisted
7. Logout and close your browser.
8. Open IE 11 and attempt to login to the OWF instance

Observed behavior

The access warning dialog does not appear. Instead, the user is presented with a screen that contains only OWF's background pattern. No menus, controls or dashboards appear.

Probable Cause

webapp/js/app.js calls Ext.util.CSS.createStyleSheet(css); when the backgroundURL is set. This invokes a call in the underlying ExtJS framework that is not compatible with IE 11. This line should use another method of modifying CSS.

See 2318ef8 for related work.

Workaround

1. Clear the backgroundURL field
2. If a backgroundURL is still required, this can be achieved by replacing the default background file in the common directory for themes.