5 volt GPIO power pins broken – Raspberry Pi Forums
The GPIOs are protected by internal diodes, normally reverse-biased and connected to the power rails – 3v3 and ground. In the case of “5v –> 10k Pull-up Resistor –> GPIO –> Button –> GND”, when the button isn’t pressed, current from the 5v through the 10k goes into the GPIO and through the internal diode to the 3v3 rail.