I’m guessing that you were bitten by this bug:
I suspect that you didn’t do it correctly. Predial hook is after the bug so should have worked.
Were you doing this via DTMF or another unusual way? On a normal IP phone (or softphone, SIP app, etc.) when you press the Tran key, the current call is placed on hold and the phone makes a new call. Asterisk isn’t even aware that this is a transfer until you press a key or hang up to complete it (which tells Asterisk to bridge the calls together). So it’s hard to imagine how this bug could have manifested itself on a ‘normal’ transfer.