Clicking the LinkedIn logo loads the Google+ sharing.
We used the same sprite position since we had the offsets in the CSS for where LinkedIn used to be, this was a big time saver across all the site themes. Buuuuuut, we missed some sprites: Stack Apps and Server Fault.
A build is rolling out now with new sprites and cache breakers to resolve this.
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 looks like they just updated this to include G+, and get rid of LinkedIn as per this screenshot:
If you refresh or wait a little while, it should change.
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.
The logo changed to a little
g+ icon for me when I reloaded this morning. You can see it near the bottom of this sprite:
I assume you'll get the updated sprite soon.