Seen something like this before in a block of flats where lowest bidder contractor installed 'two tv sockets' in every flat.
Both were full spectrum outlets so B2/DAB/UHF and sat on each socket. If you terminated one socket with UHF and tried to use a passive splitter to a Sky+ box the latter didn't work. For an extra £30 at installation said contractor would install a socket in the bedroom, that was nothing more than a faceplate and patch lead going back to the 'master' dual faceplate rendering Sky+ unusable at that socket. This was in Eastbourne but ISTR contractor were from up Milton Keynes way.