In the past I had to burn the bootloader sometimes to make a bricked Arduino working again. I didn't have to do that for a long time.
But today I corrupted the bootloader. I accidently connected a plug upside-down. It should not blow anything, because there are resistors to limit the current. Only the SCL pin got a negative voltage, but luckely the SCL pin was still okay.
The sketch was still working, but I could not upload anything. The fuses had not changed. After burning the bootloader, everything was okay.
This is not normal. Why did the sketch still work, but the bootloader was the first thing to go ? Why could a negative voltage or perhaps a negative pulse or glitch corrupt the bootloader at all ? Is it cross-talk inside the ATmega chip, or was wrong code executed ?