Tested this behavior in Opera 22.

Steps to reproduce

1. Download "Clockres.exe" from Windows Internals (http://technet.microsoft.com/en-us/sysinternals/bb897568) to view timer interval.
2. Close other browsers including Opera if running.
3. Open Clockres.exe in cmd.exe and note down the Current timer interval.(Should be 15.6ms if the PC is idle)
4. Open Opera and load any site.
5. Note the Clock timer interval, System clock tick rate is increased to 1ms
6. Minimize Opera(idle), still the clock tick rate is 1ms.
7. 1ms tick rate is left forever (until browser is closed)

The issue has been reported on July 18 2014. No solutions yet.