It is way too easy to abuse the self-voting system. It's great that many users aren't abusing it, but in the long run it seems like a big weakness that anybody can just start voting for themselves nonstop if they want.
I don't really know what solution can be done that would fix it, though.
Seems like the simple solution is just don't allow self-voting, there are some pretty obvious workarounds, but this would be at least a partial fix.