Using a TinyAVR, I have the same problem, and this infinite loop:
CMD: [ac a4 00 01] [00 ac a4 00]
CMD: [50 08 00 00] [01 50 08 f9]
CMD: [50 08 00 00] [00 50 08 f9]
CMD: [50 08 00 00] [00 50 08 f9]
CMD: [50 08 00 00] [00 50 08 f9]
CMD: [50 08 00 00] [00 50 08 f9]
CMD: [50 08 00 00] [00 50 08 f9]
CMD: [50 08 00 00] [00 50 08 f9]
CMD: [ac a4 00 01] [00 ac a4 00]
etc.
So I don't think it's "ArduinoISP" related.