In Istanbul, the navigation and homepage don't load and the instance fails.
Steps to Reproduce
Navigate to User Administration > User Preferences and select the preference named tabbed.forms.
Make sure that the System checkbox is selected.
Type True or False in the Value field using a capital T or F, and click Update.
Log out and log back in again.
On Helsinki, none of the homepages load. On Istanbul, the navigation and homepage don’t load and the instance fails.
When creating or updating a user preference whose type is true | false, use only lowercase letters.
Related Problem: PRB820893