Wow, taken a while for a reply on this to come up...
I'm using my own mildly modified version of a ROM given to me by a Kobo dev, which I assume to be the latest version of the firmware they've publically released. Issue happens to me with just that base ROM itself, it's not my modifications causing the problem.
I've just learned to avoid it by not pulling the bar down too far - consequently I haven't seen the problem in ages, but it's definitely still there.