This is a known issue. Windows 7 does not apply customized power plan policy created by Group Policy Management Editor.
Repro steps: (w and w/o SP1)
1. Open group policy management editor=>computer configuration=>preferences=>control panel settings=>power options
2. Create new power plan, in ACTION column, choose “Create” option
3. In next column choose either of the build in plan, choose “High performance” as an example.
4. Check the “set as the active power plan”
5. Customize power plan settings
6. Click ok the finish policy setting.
7. In windows 7, restart computer to apply computer policy.
8. Open power option, you will find the “High performance” box is not checked. But customized settings such as idle time are applied.
Note: this problem also exists in user configuration.
In the new power plan properties, there is four options in ACTION column “create” ”update” ”replace” ”delete”, choose the “update” option instead of “create”, then problem will not occur.
Do not choose "Create" or "Replace”, instead, choose "Update" then it works fine.
Read the following article. At the end the behavior of Replace/Update/Delete/Active is explained:
Managing Power with Group Policy: Part 3 of 3