I had the same problem at BNE
I was in Brisbane for one day (not MR) for a business meeting and was held for over an hour and a half two weeks ago. Part of my problem was one way from LHR - SIN - BNE (SQ)and then out the next one way BNE - SYD - LAX (UA).
On top of that, I had an unopened bag of gummy bears which I did not know needed to be declared... That 99¢ bag of candy cost me $109 fine. Not sure what the difference is between gum, mints, and gummy bears, but they didn't fine me for the mints and gum.
Moral to the story - Declare ANY and ALL candy!