Possible Lich Bane Bug?

Lich Bane seems to be causing some REALLY weird interactions. I picked Ornn in practice tool, maxed level, maxed gold, stopped minion spawning, spawned a dummy, and activated CD refresh. I then checked the damages for tri, then iceborn, and then both. Afterwards I remembered that lich bane also shares the unique passive so I checked that too which is when I found these numbers. It seems that lich bane is severely reducing auto damage. It doesn't seem to be intentional since unique passives are supposed to choose the best parts AND the lich auto (buffed and base) are lower than base damage without Lich Bane despite me having 89 ap. Here's what I put into my notepad as far as base and buffed auto damage with and without the items. Is this a bug?

No Items 66 base auto damage

Trinity Force 79 base auto damage 206 buffed auto damage

Iceborn Gauntlet 66 base auto damage 130 buffed auto damage

TriForce+Iceborn 79 base auto damage 206 buffed auto damage

TriForce+Iceborn+Lich Bane 76 base auto damage 76 buffed auto damage

Lich Bane 64 base auto damage 64 buffed auto damage