Hello. I've assembled a Diavolino and powered it up with the USB-TTL cable. After that I've uploaded a sketch to it and it worked fine. Everytime I try to upload a second sketch to the board, it fails, getting this:

avrdude: stk500_getsync(): not in sync: resp=0x00
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

Then, to upload the new sketch I have to disconnect the cable from the PC, plug it again, and then re-upload sketch.
Is that normal behaviour ?

Thank you

This happens on Windows machines.

Try adjusting your port settings to end the pain: Device Manager - Comm Ports - USB Serial Port - Port Settings - Advanced button - Set RTS On Close.