Yes, I'm using the Optiboot bootloader, and fuses are set accordingly, E/H/L L/H/E = 0xFF/0xDE/0x05. And I get the same result whether I burn the bootloader from the Arduino IDE, or do it myself with avrdude. Have done this successfully multiple times, with several chips, using both methods, so I'm fairly comfortable with the process. It's just this one chip...