Unit 013 BT-8 has wrong class - assault gun, resulting in it appearing in StuG (Ryynntyki) formations. All BT-8 Finns had (4 of them) were used together with BT-5 and BT-7 in one battalion. StuGs were never mixed with those tanks.
I just d/l'd the patch and installed it, the BT-8 still turns up in StuG formations.
I think the problem is that both BT is assault gun AND the formation are set to use it by default (I believe somebody mistyped unit 13 instead of 23 in StuG formations).