5kVA48V Hybrid Inverter

I have installed a few of these Systems. The System is connected to 10 x 320W Modules with 8 x 180Ah12V AGM Batteries. The Inverter is also connected to the Utility. The System will give power to the Loads and when the Batteries are at 50%, it pulls in the Utility. At this stage the lights, fridge etc. dips. Why does the Loads dip as everything gets its power through the Inverter all the time. It's only the Supply ( Solar, Battery and Utility) that changes?