Not a bug but,
lvl 350+ /w donation mana rune: 779,774,778,788,777,744,796,790,778,797,788,787,765,789,776,795 (avg ~781.3)
lvl 350+ /w mana rune: 713,707,686,749,675,763,714,757,708,742,672,685,755,750,671,732 (avg ~717.4)
Plus/Minus = ~65 mana. :ninja:
You should update donation page or tweak mana rune formulae.