Believe it or not, the capacitors I mentioned are absolutely necessary for stable operation of the Atmega! It may be that the Atmege, as long as it is connected to the USB-ASP, gets a sufficiently clean operating voltage, only if you pull it off and supply your board via the DC socket, things look completely different! The processor doesn’t care whether it has seen a clean operating voltage while flashing, if it no longer has a clean voltage afterwards, it cannot work properly, regardless of what happened before.