Blizzard is extremely dumb and forgot to update their API upon introducing Horde vs. Horde battlegrounds in WoW Classic TBC.

There's an edge case where if you are disguised as alliance/horde, a victory or loss will be recorded as the opposite on BGHistorian. For example if you are a Horde player, disguised as alliance in a battlground, and lose the battleground, it will appear as a win on BGHistorian (because technically a horde team won). The API function GetBattlefieldWinner does not specify if the BG is a same-faction battleground. Therefore the only way to circumvent this is to check for the disguise buff upon the battleground ending.

This bug taints the data recorded by BGHistorian thus making the addon completely useless.

Fix live as of a420c3c

Thank you @LeoMelnyk

Closed.