Now since from October there is the new airside transfer bus between T4 in addition to T2 and T5.
The stupidity is that you cannot go from T5 to T4, but from T4 it works nicely to T5 gates 11, 10 and F5.
I tried the other day to enter from T5 towards T4 but no no, the driver said it is due to "toll rules" which is complete nonsense, why would you otherwise be allowed to take the bus from T5 to T2 and then from T4 anywhere?
Oh well