staggered discount not working right

[atsites]

Hi people

PS has this wonderfull option of "staggered discount''. (tab 6)
For instance, when ordering more than 20 pieces of a product one can automatically configure a percentage disount.
When 40 pieces a higher percentage, etcetera.

I discovered that this feature works fine, but when ordering whitin the same article different combinations of colour or size
the discount will not effect.

For instance, made a staggered discount of 5% by a order of 20 products.
When ordering this article in the shop 12, size M, and 12 size L, the discount is not working, even when this number of 24 is exceeding the 20 configured.

Anyone familiar with this ? A bug or perhaps a workaround available ?

Like to hear

Jan.