Topping from the bottom
For some, this phrase has a negative connotation, implying that a person wants to "play at" the role of submissive without truly yielding control. For others there is no such connotation — particularly when someone is a spankee or otherwise a bottom, but is not (and does not pretend to be) in any sense a submissive. For people primarialy into sensation play, it seems natural for the physical receiver — the bottom — to direct the course of the scene, at least on some occasions.
The varying views of this phrase combine with the varying views on the role of the bottom. For some "bottom" more or less implies "submissive", or at least such people believe that these two roles should always be linked. For others, "bottom" implies strictly the physical receiver, and may have nothing to do with submission, dominance or any form of power exchange.