sorry, the default actions for buttons still happen, no matter where you do this.

adding an option to disable them is one of the three high priority features for a future release. {the other two are media volume control, and quick-snap pictures from lockscreen}. all three require figuring out some rough stuff, though.

on the regular lockscreen, volume keys change the volume when music player is running. when its not, they change the profile. on the lowpower lockscreen, they do nothing by default.

you might want to consider using the lp lockscreen as a workaround for this missing feature; there are no default actions there. i personally have the power button unlock both so that i never see the regular lockscreen. {i use lpsmagic to make the low power screen useful; it shows battery % and discharge rate, and my currently playing song}