Randomly my dock icons will show the default application icon. Sometimes they return again. I have previously reset the dock and deleted the .plist, which temporarily corrects the problem, but it returns soon enough. Removing and adding the app to the dock again also restores the icon, until the next time. It's tiresome to do this all the time, obviously.
The apps usually affected are the default Mac OS ones. The above screenshot shows my current situation: Mail, Safari, Reminders, iTunes and Terminal are not showing their icons.
I didn't find much on Google by way of people complaining about similar behaviour. Is anyone else suffering, and can anyone suggest a more "permanent" solution?
Thanks in advance.