Programming arduino with an external programmer

1) Arduino is connected with usb tiny, our external programmer.
The external programmer is connected to the PC .
We upload successfully the arduino blink sketch but we lose the bootloader.
2) We connect arduino directly to the PC.
The external programmer is disconnected from arduino.
We can see that we are not able to upload any sketches.
3) We reconnect the programmer to the PC and the programmer with the arduino board via the ICSP header.
We burn the ATMEGA with our new bootloader.
4) Now if we connect arduino directly on the PC removing the usb tiny we can upload our sketches normally.

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