I'm not completely sure this is a bug, but it seems
like it most likely is.
Currently the system sidepanel summary of the resources
produces by a system includes the resources produced by
planets owned by races other than the player. Since
systems in which you don't own any planets don't show
this information, I'm guessing this shouldn't happen.
I suppose you could explain it by saying that if you
have a planet in the system, you can watch the other
planet and thus know what it's producing, though one
might also say you could do that with a ship in the
system for a whole turn as well...
Anyway, I assume you'll know whether this is supposed
to be the case.