I just stumbled about an approval calculation error:
(Edit: see external link, inserting of dropbox link here doesn't seem to work)
According to this image approval is calculated as follows:
Harmony Crystals + Supportive Population + Easy to Please + Colony Capital = Base Approval = 3 + 4 + 4 + 3 = 14
Base Approval - Large Empire Penalty = Effective Base Approval = 14 - 15,4 = -1,4
Flag Waving + Entertainment Capital + Approval Relic (3) - War with Favored Civilization + Scenic World = Bonuses = 20% + 25% + 150% - 25% + 25% = 195%
Effective Approval = Effective Base Approval * Bonuses = -1,4 * (100% + 195%)/100% = -4,13
So you see that bonuses do amplify negative effective base approval what is wrong in my opinion.
A more logical approach would be to first calculate Base Approval * Bonuses and then subtract Large Empire Penalty:
14 * (100% + 195%)/100% = 41,3 - 15,4 = 25,9