Clicking the LinkedIn logo loads the Google+ sharing.
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I headed over to Server Fault to check the sprites, as Tim hinted this might be the source, and can confirm that the LinkedIn icon is still present. You can refresh all you like, alter the version query value, it's definitely still there.
After going through the full list of sites over on the Stack Exchange site, I can find no others where this occurs (I think all beta sites use the same one, which I only thought to find out on the last two).
It shows a Google+ icon there for me. Perhaps you're using an old version of the CSS sprite image? If you look directly at the CSS sprite image, there is no LinkedIn icon there at all.