If it's anything like the Prius (and it's pretty close!), there are computer algoritms that control the whole energy system, to keep it optimized, even at times running the gas to maybe get the engine back up to clean emissions temp, or to top off the battery when the power requested from your right foot says there's extra energy available to charge and not needed to propel you forward.

I know at times my Prius runs the gas when I'd like it not too (similar situation as the above poster). But, I chalk it up to the system knowing what it has to do in order to keep everything efficient, etc. Smart cars!

PS In the Prius there are 5 stages of hybrid operation that happen, depending on many variables (temp, battery charge, time spent stopped, time spent warming up, etc.) Do a search on Priuschat or Priusonline. It's pretty amazing the software built into the Prius (and the like Escape hybrid) that controls energy, giving you the best efficiency and performance.

'04 Seaside Pearl #7. Fumoto oil drain, mudflaps, rear bumper scuff protector & rear warn system, compass mirror, EV mode button, 8" subwoofer in right rear cubby & 6" subs under seats, power lumbar in the front seats, Coastaletech hitch w/ Aspen bike/snowboard rack. iPod2car, 2 amps, Alpine component speakers, and DVD video, solid 47 MPG @ 70000 miles.