Have you tried different flip-case on that phone?
Sounds like it could be a misplaced magnet on the flipcase since when you move the case over the screen the phone does work and go into standby.
Thanks for your answer. We have two DTEK50 and 2 Flipcases.
On one DTEK50 the two cases work fine but on the other DTEK50 no case works without moving over it.
Is it possible that the sensor in the phone ist misplaced?
I think the original cases work best. When my z30 case broke I purchased another from Amazon. Even considering the eol of the phone, I was surprised at how inexpensive a new bb case was. But I debated if it was a second quality or fake BlackBerry z30 case. While I don't know if either of the above is true, what I do know is that my replacement case does not put and keep the phone in standby mode as well as the original.