heavy tank in medium tanks

That's interesting the Kv-1 is a Heavy Tank and the Kv-1b which is what is listed in the Research Tree is still considered a Heavy Tank and the 1st heavy tank is a Kv-2 the correct tank their should be a T-28 then it should branch off.

and also the BT-7 is a light tank (today known as IFV)

and its in medium tanks when it should also be in light tanks