I too have been caught up in the OP mess and (naively) thought they were a traditional online broker with a margin lending facility which I rarely used.
After I setup the account I transferred some existing issuer sponsored stocks in so I could trade them at some point. Here's a question though. If it's true that in doing so I have forfeited ownership of those stocks at what point is the CGT event triggered? If I no longer own them, then at what price did I sell them to Opes Prime for? The only form I filled in was a "Collateral lodgement from sponsored holding (HIN)" which specified it was a "005 off market transfer" to ANZ Nominees which I assumed at the time would put the shares in a trust account. The form did not specify at what price the shares were being transferred at. If it did trigger a CGT event then why the hell didn't someone at OP let me know this was going to happen?