How to swap item slot rows?

[LintMan]

A couple of times now while playing, I've discovered that the bottom row of usable items (the hotkeyed ones) has been suddenly swapped out for one of the other rows.  (ie: the topmost row of items is not the bottom row and vice-versa.)  I have no idea how this happens, or how to reverse it, so I then have to individually swap the items back to their proper rows.

Does anyone know how this works?  Thanks!

[Oralordos]

I believe that function is bound to the "R" key by default.

[Coppermantis]

Yeah, it's R to switch. It was really annoying when it would randomly switch upon loading and I didn't know how to quickly reorganize.

[LintMan]

Thanks, guys!

[Terraziel]

For the record there is also a key binding for switching ability bars the other way (so scrolling down rather than up) which i think is blank by default but which is pretty much a necessity if you want to use multiple ability bars.