Happens when mixing looped animation with non-looping and application lags heavily (dt in update() is big) (which happens all the time when running in iOS Simulator with good load).
m_pLoadingBG->setAnimation(0, "idle", true);
... somewhere later...
m_pLoadingBG->setMix("idle", "map", 0.5);
m_pLoadingBG->addAnimation(0, "map", false);
As result - animation freeze at some frame.
Looks like it freezes anyway if mixing is set - just tried it on device.