The buddleia madagascariensis is described in the book put out by the Royal Horticultural Society, "Buddlejas" by David D Stuart....on page 45, theres quite a long description, over half a page, but part of what it says is its a worthy species and would be good choice for a large conservatory or against a warm wall in the garden....and it received the Award of Garden Merit from the Royal Hort Society in 2002.
It originally came from Madagascar.
The flower starts off pale yellow, then develops into a really deep goldy yellow with age, and has a strong honey scent.
(I have lots of photos of it, or you can google images of it)
The two plants that I know of in Nelson, don't seem to be a problem, and it flowered late winter, and is still going now.
I am like Charlotte, growing most of mine in pots/buckets until I decide whether to give them a permanent spot in the garden.
The butterflies are clambering all over lilac coloured buddleia flowers on the one thats flowering at the moment....in its pot.