There may be some Sonar setting - I do know that there is a picture cache file that you can find under Preferences, but do not think that is what it is for - might be worth looking at, but doubt it.
Do you have any issues with other icons? There is sometimes unexplained corruption of the Windows icon cache, which is sort of a shortcut Windows builds to save from having to scan all docs and apps to see what kind of icon to display for them. This can and does sometimes get messed up.
There are multiple methods of correcting this, you can look it up - I would recommend NOT downloading someone's free batch file or program to do the rebuilding of the cache, for obvious reasons.
One such article, coming from Microsoft, gives you an explanation of this, but might not be correct for your OS version. The issue is the same across all versions, but there may be differences in the steps to take.
If memory serves, you can try stuff like restarting, or changing icon size and then changing it back, or you can locate the iconcache.db (shelliconcache.db maybe) and delete it, and restart Windows, and it will rebuild it. But read the article first, and in your search terms, add the specific Windows version you are using, to get you the best list of articles to choose from/
Here is one such article, but it is from 2007, but it at least gives you an explanation of things:
http://support.microsoft.com/kb/Q132668 I have rebuilt mine before on 2 occasions over the years, and did it both times by locating the correct iconcache file and deleting it. There is a bit in that article of upping the maximum number of icons maintained in the cache, I think the default is 500 or 512. You will see when you look it up.
It certainly will not hurt your system any to rebuild this, providing you use Microsoft steps for the OS version you are running/
Hope this helps,
Bob Bone