Pixl LCD initialisation and output

After quite a while of Espruino abstinence there is a new private project for me: a bicycle computer.
When uploading code, doing a save() and a power cycle there is still the Pixl logo showing up before my code takes over the screen.
Also when connecting or disconnecting via bluetooth sometimes output shows up for a fraction of a second.
Where does that all come from - can it be disabled or avoided?

Thanks for any pointers.