The problem appears to be the library using Serial Port B with the clk on PB0. I hooked up a scope and saw clock activity on the line even with my SPI routine disabled. Something else is periodically clocking 2 bytes. The literature says the serial flash uses the line at INIT, but not after. Something is using it though. I wrote a bit-bang routine and used PB4 for the clock, works like a champ now.