Hm yeah, don´t start to think.
I used an older SPI-configuration with screwed clock polarity settings.
In case any ATMEL user´s find this topic:
CPHA and CPOL Bits in the SPCR register must be '1'
CPOL = Clock Polarity (1 = high on idle)
CPHA = Clock Phase (1 = sample on leading edge)
> Topic can be closed