What dwarf are you talking about? Teddy bear? Lil gem?
It sounds like nursery guy'll say anything to sell trees during the off season although technically smaller leaves and smaller trees means smaller mess.

Any Magnolia grandiflora will drop parts in ones and twos during summer. Deciduous magnolias, on the other hand, drop their leaves all at once in fall. Their tepals ("petals") fall all together after the mass before-the-leaves spring bloom with those popular kinds that produce this. Deciduous magnolias from other groups, that have a more scattered opening of flowers after the leaves expand will also have a more scattered shedding of spent flower parts.

Monrovia is using "dwarf magnolia" for the 'Little Gem' cultivar of M. grandiflora. This would not offer an escape from the littering behavior of all examples of the same species.

Popular small-growing deciduous magnolias are lily magnolia, star magnolia and the Kosar and De Vos hybrids between them produced by the US National Arboretum.

thanks for the info. I think it was Little Gem. I think we'll have to rule this out.

See table of Patio Trees starting on page 79 of the Sunset WESTERN GARDEN BOOK (2007, Sunset Publishing, Menlo Park):

"All produce minimal litter from flowers, fruits, leaves, and branches, and have root systems not likely to crack or raise pavement"

I think the leaf drop is the biggest complaint about southern magnolia. Leaves are a good bit smaller on lil gem than full size cultivars but they're going to drop.