Thumbnail previews for edited pics not displaying properly

I'm running W7 64-bit and using Faststone as my default image viewer/editor. If I change the hue of a picture from, for example, brown to blue, the thumbnail for the new blue picture remains brown instead of changing to reflect the new color. This is frustrating because I don't know what half of my pictures look like until I click on them. Why would the thumbnail not look like the picture it represents? Any help or suggestions would be greatly appreciated. Thank you.

Boohbah, thanks for the quick reply. I probably should have clarified that this isn't a new problem; I have pictures that are over a year old that still show the thumbnail of the original pic. I always found it annoying but I simply brushed it off. However, now I'm beyond frustrated. And it doesn't happen with ALL pics, just some. Restarting explorer or my computer in general has no effect on the thumbnails whatsoever. I'm thinking perhaps it's a problem with Faststone (which, unfortunately, I happen to like very much), so I'm going to try a different image editor. Again, thanks for your input. I will certainly let you know if I find a resolution.