Well I never understood this sleep function as it isn't clearly defined as to exactly what it is as this differs from one OS to another. On my main system XP Pro desktop, Display Properties, Power settings, Power Schemes, there is no Sleep mentioned only Standby.
I have mine set to go into standby after 20 minutes, yet in another area, Advanced it mentions a Sleep button. I really do hate it when they give mixed terms/names etc.
However that said, if I have it in standby mode the Wake up feature does work and runs the scan.