I'm not sure if this has already come up but a lot of the links using the MID tag seem to be broken. For instance my message Message 68 contains such a link. In fact looking at them I can see that the links from the old MID tags still have the cgi version of the url rather than the php, i.e. EvC Forum: Potential falsifications of the theory of evolution .
It may be that you had given another of their messages a higher rating at some point. That means that you could have lowered your own average rating for that poster and that in turn would lower the overall average.
At least that was how I understood the system worked.
There is something mixed up with post counts for search results. The results for a query all say they have the same number of posts, although the exact number changes from search to search.