That is quite normal - when you start the car your starter motor
pulls a lot of current out of the battery, dragging down the voltage.

Depending on how much the battery voltage drops you might or might
not get the brief shutdown, while you still might get the battery symbol.

I don't recall the exact voltage levels where the indicator triggers and
where the display/output is suspended, but I'm pretty sure they've been
mentioned on the board - maybe in the FAQ?

/Michael