Posición de Always, Never, Often, Seldom, Sometimes

Always, never, often, seldom, sometimes, se colocan ANTES del verbo:

He always eats something at five
We never go swimming
She often comes in late
I seldom sleep well
They sometimes dance after supper

Pero se emplean DETRÁS del verbo to be:
Robert is never on time
She is always complaining
I am often tired
The teacher is sometimes wrong
We are seldom satisfied with the money we have