I found that using a value of 4 gave me the same symptoms as the OP, the DRLs were only on with the side lights and the side lights were faint.
I found this info on the VW Vortex site and using a value of 15 in Byte 18, this cured the problem, I have halogens.
MJ2009 with BCM (03xx software)
Encoding VCDS Byte 18 = 04
Lights go out at the tailgate opens NO
Error message MFA Rear fog lamp with Resistance: No
Problem with front parking light (weak light) NO
LED tailgate light up more when braking YES
MJ2010 with BCM from KW22/2009 (Software 0537, 0541)
Encoding Halogen VCDS Byte 18 = 15 Xenon VCDS Byte 18 = 43
Lights go out at the tailgate opens NO Update on 0575 / 6 *
Error message MFA NO Update on 0575 / 6 *
Problem with front parking light (weak light) NO Update on 0575 / 6 *
LED tailgate light up more when braking NO Update on 0575 / 6 *