It is possible to extract kernel from firmware image (flasher-3.0 -u -F firmwareimage.bin) and flash kernel over usb again, as explained in jott's instructions http://sse2.net/rotate/.

Just wondering what exact 'step by step things' you did and which kernel you flashed. If you flashed from the device by kernel_flasher and used my tarred and gzipped kernel than I don't know how this happened. The flasher checks some bytes in kernel image header and won't flash files with wrong header or shorter length. Such bad flash may happen only when header and size is ok but the zImage file is still corrupted and have some bad data inside. This should not be possible when the kernel is inside .tar.gz. At least you would see some error when extracting the archive. Still, maybe I should add some additional checking. Not sure if there is some checksum to compute and verify but maybe I could just strip the header and try to decompress the kernel via gzip somehow (kernel image is gzip compressed). That would probably catch some random corruption inside.