I'm not a solar panel installer but the first use of any power generated by these systems is as an infeed to the house. However there has to be a way of switching off the power completely to the house via the mains switch on the CU (or qualified persons would run the risk of getting an electrical shock on a sunny day).
I assume that, if one switches off the main switch on the CU, the solar panels feeds generated power straight back into the grid since the house demand is zero, but we are hardly talking of a loss of mega £££s here (in lost infeed).
I wouldn't worry about it.