That is odd behaviour indeed - thank you for raising it.
The Ken Burns is really more of a slideshow special effect and one wouldn't really be zooming in or out.
just play and let it roll...
To manage and zoom I feel you should really be turning Ken Burns off
Agreed. I only noticed it because the Ken Burns effect was on by default after I upgraded the firmware. I have turned it off but, if zoom can work, then it would make sense to enable both buttons. Even in a slide show someone might want to zoom in on some detail in a particular picture.