oh right I see it, polution modifier is not changed but energy consuption is so everything is shifted by energy not by polution modifier ... I have to say it rather confusing.
I gues its not a bug than but you might want to consider improved tooltip so its easier to understand

pollution multiplier * energy usage multiplier * base pollution

okay so unmoded furnace = 1*1*1=1
with one production module it should be chnaged by 5% so 1.05*1*1 it should be 1.05 ... ? I still cant see the 1,47 happening ?

well base polution for electric furnace is 1 so with 5% incerease it should be 1,047(or less depending on how its actualy counted) instead 1,47 (after counting speed decrease) , I have noticed this on mines when I was wondering that polution with 3 modules is over 25 ... with base 10 ... thats not ...

Label says 5% but 50% is added, happens at lest for mines and electric furnaces