Buddleja White profusion reverting

Hi there, hope you are all well,

last year we planted a white buddleja profusion which flowered beautifully and as it should ( with white flowers)

It's just started to flower again and it appears to have reverted - in fact there have been no white flowers whatsoever so far - all purple.

Is there a way of stopping the reversion process or is it ( as i suspect) too late?

I've also noticed this year the plant has trippled in size. It's getting on to about 8 ft - an absolute monster compared to last year.

we also have two other buddleja near by to it - sky blue and dark knight - not sure if this may have effected the white profusion in any way?

any advice would be greatly appreciated. 

Thank you,

Jack.