Ann: First Half FY2018 Results Announcement, page-3

It's not conservative per se, it's just the way it is with software companies - they get paid up front for project work and record a deferred revenue liability, then the revenue is subsequently earned through the P&L and the deferred revenue liability reduced off the balance sheet. OCL tends to get paid in 1H, then do the work in 2H, so what you see in 1H is a jump in deferred revenue liability / operating cash flow (or receivables), then in 2H revenue jumps but operating cash flow lags and deferred revenue liability will drop by 30 June.