ENC28J60: Invalid CRC in wireshark when transmitting packets

I just playing around with the ENC28J60 Ethernet controller from Microchip, but when I send packets with the controller, Wireshark reports a invalid checksum. The CRC field is always 0x00000000.

This is in my initialization for the MACON3 register:

write_reg(BANK2, MACON3, (1 << MACON3_FULDPX) | 
                         (1 << MACON3_FRMLNEN) |
                         (1 << MACON3_TXCRCEN) | 
                         (1 << MACON3_PADCFG0) |
                         (1 << MACON3_PADCFG1) | 
                         (1 << MACON3_PADCFG2));

When I send a packet, I set the PCRCEN flag in the control byte.

I have read the errata document of the the ENC28J60, but I can't find any information about a invalid checksum calculation. The revision of my chip is B7.

Is there something missing?