I had to go to Wikipedia to find an answer:
http://en.wikipedia.org/wiki/Flag_of_AustraliaScroll down to the bottom of the History section and you have this:
"In 2002, the leader of The National Party of Australia, John Anderson,
proposed to introduce laws banning desecration of the Australian flag,
a call which attracted support from some parliamentarians both in his own
party and the senior coalition party, the Liberal Party of Australia.
However, the Prime Minister, John Howard, rejected the calls, stating
that "...in the end I guess it's part of the free speech code we have
in this country." Trish Draper tabled a private members' bill in 2003
to ban desecration of the flag, "Australian Flags (Desecration of the
Flag) Bill 2003. John Howard did not support the bill and it was never
brought before parlaiment."
I have a sneaking suspicion that Howard didn't support it simply because
the numbers against it would have been overwhelming, but now that he
has the majority needed to get such a bill through, I wouldn't be a
bit surprised to see it surface again.
But in the current case, I would guess the prison sentence is for
whatever else it was that he was charged with.