Not really weird at all. Just means you have a great Sky signal and a lousy Freeview Terrestrial signal.
I find it strange that both come from the same socket. Is there actually a UHF antenna connected anywhere or are you trying to run UHF off the Satelite Dish?
Check with the building manager/body corporate to find out how the signals are distributed and how to fix it.
If the signal is coming from the same socket, then you must have some form of signal splitter in order to get the signal to both the Sky STB and Freeview TV/STB.
Try feeding the signal directly from the wall socket to the Freeview TV/STB to see if it is still bad, and if so try another cable if you have one. This can then eliminate any issues caused by your cables and/or splitter.
Hi, as others have said its not unusual but normally there are more bits to the puzzle. So I assume you are testing these with both connected at the same time? or separately.
If at the same time, what are you using to split the signal, if its just a simple splitter then its possible that the Sky box is not providing an ideal impedance at 500-600MHz and crimping the UHF signal, a proper Sat/UHF-VHF diplexer would be better, but all depends on how this is setup.