FWIW, I had this happen yesterday, first time I've ever seen it. It happened on a project I started with a project template if that helps. There was no degradation of performance but it bothered me so I just reloaded the icons. I'm getting ready to work on the project again this morning, it'll be interesting to see if it happens again.
I'll empty the picture cache before I start just for giggles.

I can hardly see the darn things anyways, so I wouldn't know the difference.  :)
 
Bob Bone
 

Oh WOW man...like...I've seen it tooooo.
 
I suspect that it might something to do with the transparency layer in some specific icons.  For instance, I have a drum kit icon (Drum Kit 1.bmp) that often gets messed up.  Most other icons that I use regularly don't have a problem.
 
It may be helpful to have affected persons list the filenames of all the icons that experience this issue and then have someone who knows a whole lot more about graphics formats and display issues than I do, look for commonalities between those files.

Deleted Picture cache with no observable difference.
 
Ran a couple of tests. I loaded icons to tracks in a project and they looked fine; I saved and closed the project and reopened it to find all icons except track 1 were pixelated with a grey halo. I reloaded the pixelated icons; closed project then re-opened and icons fine.
 
I then modified the test by only reloading one or two of the pixelated icons, leaving some still pixelated. Upon reopening the file the previously reloaded icons were fine and the icons that I had not reloaded were still pixelated.
 
In each case track 1 icon was always good. I varied the icons I used for the tests (though whenever I reloaded an icon, I always used the same one as the one replaced).
 
I also tried using a template I made that I had saved icons to. The same scenario: when I open the template the icons are pixelated with grey halo, except track 1. If I reload the icons, save and close the project and reopen, all the icons are fine.
 
My screen resolution on a 22" PC monitor is at maximum: 1680 X 1050.

Sorry you are experiencing this.
We'll look into it.  
 
Couple of clarifications/etc...
Firstly deleting the picture cache has nothing to do with general graphics.  The picture cache contains data specific to waveform overview files (wave pictures) nothing related to graphic images used by the program.
 
Second, are there particular image attributes that are in common with what's corrupted?  i.e. using 1024 x 1024 wahzoo files or something.  Not that we support a wahzoo format, but curious if it's any file or particular files.
 
Third, I wonder if there's something using up graphic resources (you can check the count of gdi handles in task manager).  Those types of issues exhibit over time (sometimes a long time).  In Win 8's task manager, click on the details tab, then right click the header Name, PID, Status, etc. appear and choose select columns.  Pick GDI Objects from the dialog that appears.  Now take note of the count.  Around 10,000 Windows will shut down a process.  Near that and things could start to get weird.
 
Best bet would be to coordinate with support.  However, these were a couple of quick thoughts I had about this.
 
Keith
 
 

And update your display drivers/run windows update.

I see this all the time in my SONAR system.
Maybe it's connected to using track templates. Maybe.
 

Standard SONAR shipped icons get pixelated, not just my custom ones.

This really smells of bad display adapter driver...

Indeed. I have the problem too and I am only using the standard  Cakewalk icons that were designed for this! I did some troubleshooting and noticed that not all icons are affected. For instance the icon of the black snare will always get pixelated when loaded in a fresh project.
 
Follow these steps: Create a new project. Load the black snare icon for a wave track (don't know the image name but there's only one black snare). Then save the project and close Sonar completely. Reboot the PC and reopen the project. On my PC the icon is always pixelated. Loading the icon again makes the problem go away. As if something needs to be set right somehow.
 
I disabled transparency and then the icon will not be pixelated.... but.... if you follow the steps like before the icon will show a bit smaller then when it was initially loaded! I think this resizing is also the cause of the pixelation.
 
So... that's what I found. Hope it is usefull info for Keith.
 
Best regards,
 
Rinie