a question about voice vista: Issue with beacon when phone is locked in pocket

Hello, I have a problem with my beacon's performance. When I lock my phone, put it in my pocket, and walk, the beacon seems not to work. But as soon as I take the phone out of my pocket, it works again. Also, if I unlock the phone and then put it back in my pocket, it works as well. When I lock the phone and put it in my pocket, it announces the distance while I walk, but the sound that indicates I am moving directly towards the beacon is not played. Is this normal behavior?