I have never seen this before, so it may simply be that the user that happened to cause it had an unfortunate number for reputation and badge counts, that corresponds to a number format the Skype plugin matches (on Chrome at least).
Here's a question in which I can see the problem (viewing in Chrome, and I guess this will probably only be noticeable while the user has their current level of rep and badges).
Is there anything that can be done to prevent this in the future (and is there any point, as I'm pretty sure it's going to be a very rare occurrence?)
Disabling the Skype plugin, the question returns to normal:
Indeed, since the user has now increased in reputation (+2 for accepting an answer to that very question), the problem no longer occurs. I don't really think it would be worth looking any further into this as it must be a pretty unusual occurrence.
I have just run into this again, so perhaps it happens more commonly than I first thought. I know this has already been marked declined, but I still think it's worth pointing out: