As I interpret page 32 of the Reference Manual, "Loop Recording" and "Overdub Recording" cannot be turned on or off manually; instead, the keyboard handles this automatically (see below). Also, they are not either/or modes that you must switch between-- e.g., the "Overdub Recording" section on page 32 specifically refers to overdubbing while a Main section is looping [EDIT: which indicates that looping and overdubbing can be in effect at the same time].
Loop recording occurs automatically if you're recording a Main section, but does not occur if you're recording an Intro, Fill In, Break, or Ending. This is determined by how the different types of style sections are played by the keyboard-- Main sections are looped, whereas all other sections are not looped.
Overdub recording occurs automatically and is always in effect, with one exception-- if you're creating a style based on an existing preset style, you cannot overdub on top of a non-rhythm channel's preset data (because there is a flag inside the style which prevents that). Thus, if you record something, but then wish to re-record it from scratch rather than overdub on top of it, you must first use the Delete function to erase the data you've already recorded-- or use the Rhythm Clear function if you're working on a rhythm channel. And if you want to record to a non-rhythm channel, you will not be able to do so until after you've used the Delete function to erase that channel's preset data (if you're working from one of the internal preset styles).
That's how I interpret what the manual says. Someone who has experience using the Style Creation feature can verify whether or not my interpretation is correct.
