Most of my flights this year so far (home base Melbourne) have been calling priority first and ensuring that any not entitled are redirected to the general boarding queue. On one occasion they were called almost at the same time with both lines boarding simultaneously. Though there was a slight delay in flight time due to aircraft arriving late, so this may explain.
On 2 occasions where it hasn't happened in the past few months, has been when there have been a few requiring extra help whilst boarding. These people have been ushered through with their required assistance, then it has been a free for all for everyone else. I suspect time constraints have necessitated that.
I don't stress too much. We all arrive at the destination at the same time and generally don't require overhead space. Overall, I think the staff do a great job.