A pity about the conflicting advice, and public service policies can often a little difficult to interpret. Personally, I'd follow the advice of a senior HR person over many others (I'm in Qld public service also).

All I can tell you is that when I started mat leave with DS1 I was on a temp secondment (higher duties) that was due to end approx 4 months after I started mat leave. But as my contract was only/exactly 12 months, they paid me mat leave at my substantive level. Wasn't bad money, but the few extra $$ would've been nice too.