It seems I do a bit more damage, that would reflect from me having 125% vs 146% rise wizardry damage. So that would probably mean It is indeed only a visual bug.
However I was expecting a bit more damage, since I am wielding a 2h sword(40% increased damage) vs a 1h sword.
I did some additional testing on the worm with skill "flame" and these are the results:
No weapon & No Satan - 22560 exc dmg
1h sword 125%dmg & No Satan- 53000 exc dmg (2.35x damage compared to no weapon)
2h sword 146%dmg & No Satan - 59000 exc dmg(2.62x damage compared to no weapon)
2h sword 146%dmg & Satan - 73600 exc dmg(1.25x damage compared to no satan, 2h weapon)
Having these calculations in mind it seems that the 25% damage from satan is being taken into account, but not the 2h 40% damage buff MG's are supposed to get?
Thanks