Windows 7 Enterprise
You're on a Domain Controller and you logon to your system using Active Directory, right? :)
You're not the domain administrator, right? :)
Short answer: it's probably Group Policy for IE.
Windows Components\Internet Explorer\Internet Control Panel\Advanced settings\Searching
Registry path (Machine):
Registry path (User):
This policy setting specifies the action that will be performed when searching from the Address bar. There are two possible actions:
Do not search from the Address bar: Specifies to not use the Address bar for searches. You can still perform searches in the Search bar by clicking the Search button in the toolbar.
Display the results in the main window: Specifies that, when you search from the Address bar, the list of search results be displayed in the main window.
If you enable this policy setting, you must specify what action should be performed when searching from the Address bar. The user cannot change it.
If you disable or not configure this policy setting, the user can specify what action should be performed when searching from the Address bar.
Note that if the Machine setting is set to "Do not search from the Address bar", it will override any user group policy setting and prevent you from doing it.
It may be that your system is downloading the group policy settings from the DC and it's setting the user level setting to Do not search from the Address bar, and you keep changing it back.