This is interesting - do you know if the FTTC enabled line was installed after the non-FTTC line? Also are you sure they are on different cabinets and it's not some other reason for the lack of FTTC connectivity?
The non FTTC line is the orginal line.
I'll give a brief explanation of what i think happened.
Cab 44 non FTTC
Cab 48 FTCC
House Number 4 Cab 44
House Number 5 Line 1 Cab 44, Line 2 Cab 48
House Number 6 Cab 48