I've just got off the phone to a distraught Ashley from Two Meters Tall in Tassie. After recently tasting the beer and finding what everyone else at the SpecTAPular found - that it tasted awful - he stripped the brewery down and found a seal had gone at the bottom of the Lauter Tun!
It was allowing unfermented beer into the transfer lines and allowed some bacteria to develop. This bacteria produces Lactic Acid which produced the 'sour lemon' flavour that we all detected. Unfortunately, the flavour only develops in the beer several days after being put into the keg.
I think anyone who's been in the craft beer industry for a while will have had a bad experience of this nature at some stage.
Ashley feels terrible about it and has found the problem and rectified the situation. He has invited anyone who wants to know more to call him to discuss on 0400 777 142. I guess such is life when you're dealing with living things!