It is the standard behavior - not a bug, but a design decision.
In a normal Split, the upper part is morphable and the lower part is not. When you press Edit A or Edit B, the morphable part follows the paradigm that is used also for the same when in Single mode. That is when Edit A or B is selected, the synth automatically and temporarily morphs fully to A or B so that you get to audition the sound that is being edited. You are then allowed to use the Morph knob to be able to audition any point in the morph. The Edit A and Edit B aren't meant as performance features, an the temporary automatic morph to is meant as a helpful feature in sound design, so that you don't end up blindly editing or not knowing what the outcome of the edit is, even in a Split. I appreciate this feature, and AFAIK there has been no other reports concerning it's function.
BTW, I just want to add that I'm not putting down your suggestions, just explaining the design
