My magnum 2800 inverter/charger has a somewhat similar 'feature'. I think they call it 'battery saver' or something, and it's on by default for the out-of-the-box FLA/GEL/AGM profiles.
From the manual:
Full Charge (Battery Saver™ mode): The fourth stage occurs after four hours in the Float Charging stage. The Full Charge stage is designed to keep batteries fully charged over long periods, and to prevent excessive loss of water in flooded batteries or drying out of GEL/AGM batteries.
In this stage, the charger is turned off and begins monitoring the battery voltage; if the battery voltage drops low (12.7 VDC or less on 12-volt models, 25.4 VDC or less on 24-volt models, and 50.8 VDC or less on 48-volt models), the charger automatically initiates another four hours in float charge.