Resolution: Cannot Reproduce
Windows 7 64bit (Windows NT 6.1 build 7601 (Windows 7 Ultimate Edition Service Pack 1) i586) running Zend Server CE 5.6 (PHP Version 5.3.9-ZS5.6.0) with Apache/2.2.21 (Win32) mod_ssl/2.2.21 OpenSSL/0.9.8o with the Zend Debugger on. display_errors in php.ini set to off.
The default value for 'Display debug messages' in Site Administration->Development->Debugging changes to whatever the value of the tick box is upon refresh.
Replication steps (from screenshot):
- Log in as admin
- Navigate to Site admin > Development > Debugging
- If the setting "Display debug messages" is unchecked, check it, save settings and click Debugging in the Settings block
- Uncheck (untick) the "Display debug messages" option
- Save changes to the form
- Click on Debugging again in the Settings block
- Note change to default value