While playing a video there is an option to change the way VR Control behaves, AUTO or ON/OFF. If you select ON/OFF it won't disappear unless you look down and disable it. In version 3.50 there is a new setting to adjust the lock/unlock threshold so you don't have to break your neck :D
Version 3.50 ========== - Support for SD Cards, USB , etc using the browse option. - Improved antidrift and new gyro smoothness option for a better head tracking. - New options to adjust control size (touch and VR) and lock/unlock thresold. - Bug fixes.