Negative Diplomacy relations bug?

Example:

My diplomacy=70

Thalan diplomacy-20

The thalans have -1 in the foreign report screen for diplomacy when it should be +1 as my diplomacy is vastly better than theres.  I think the diplomacy stat being a minus is creating the bug if say there diploamcy stat was +10 then the realations would def be +1 even though -20 is of course worse.

Prob badly worded  hope the devs understand.