I have been having this issue once in a while as well and when it happens, it's a brief annoyance. Ea, I will try your idea of "helping" the flipbar back to the middle position and see if that helps when I have this issue.
Although I love my iLiad, I do wish that they had either:
(1) Used buttons like the Kindle
(2) Provided a user-controlled setting for how long to hold the flipbar for the 5-page turn
Ah, Well