Interpolated glossy problem

[lilodav]

When I use interpolated glossy reflections (for example on floor material) my objects on the floor look floating (the reflections doesn't start from the edge of the object) What parameter should I check? AA, number of samples...?
And one more thing, when I increase the number of samples of int. glossy material I usually get splotches. Shouldn't the increased number of samples improve the image?
Thanks.