I have the exact same problem (KDE 4.4.1 beta2) although without any PowerDevil norification. I have no checkmark for Powerdevil in Power Management and have it unchecked in Service Manager.
If I leave the computer unattended for 20 minutes or so, It suspends to disk and screen goes black. Hitting any key or moving the mouse activates it again after a short delay (5 to 10 seconds). Everything else in this beta version works great. This is not a deal breaker but it is annoying, especially since beta 1 did not do this. Is this a bug or am I missing another config setting somewhere. I have searched every setting in Configure Your Computer and can't find any other post regarding this behavior.
And, I should have mentioned, I don't have any screensaver activated.
I should have said, that this is on a desktop box with no power management active other than ACPI and acpid.
I can't say this for certain about beta2 (I'm running beta1), but I strongly suspect that what I'm about to post is true for beta2.
When they went to kde 4.4.x from 4.3.x, they change a few things in the area of power management control. Gone is the need to worry about power management controls in multiple locations. Now, complete power management is exclusively given to PowerDevil. This requires a new strategy to eliminate those "unwanted" power management "features" (eco-friendly computing headaches from over zealous so-called "environmental" control freaks who as "useful idiots" help to promote a specific agenda in the guise
of saving the environment. The actual scientific data is far from conclusive as to the negative effects of man made change in climate, but overwhelmingly conclusive on the miniscule beneficial effects of universally effected and enforced "green" evironmentalism -- if universal enactment and enforcement of such policies were even possible. Whoops! I'm ranting again.). Anyway...
Go into KCC:
Select Advanced User Settings
Select Power Management
In the General Settings: Uncheck
"Lock screen on resume" Check
"Let PowerDevil manage screen powersaving"
Leave the profile assignment as "performance"
Select Performance Uncheck
Set Everything except Power Button to "Do Nothing"
Set Power Button to "Prompt Log Out dialog"
Screen tab: Check
"Enable display power management Uncheck
CPU and System tab:
Set System powersaving scheme to "performance"
Save your settings. Reboot.
Your power saving should now act as you desire.