@mstefanski: It's the default (well, not exactly, but unless you want me to start rambling about e-ink internals...) on the K4/K5. 5 pages of flash-less refresh, then a full refresh. You can *disable* it on the Settings page (ie. always flash).
Keep in mind that this heavily depends on the temperature of the controller. It will fall back to full flash if it's too hot.