May not be related, but a recent install of PowreDVD 6 did exactly the same. Associated all my media icons to PowerDVD (without asking). No matter what i tried, they would not change. The media still opened in the correct app, just the wrong icon. Only thing i did not try were any registry changes. Uninstalled PowerDVD and the problem went away.
Try having a look in tools/folder options/file types and see what app that particular icon belongs to. It may reveal a clue as to what causing the problem.