Lumia 630 display turns off

[vaib04]

my phone (L630) doesn't have proximity sensor, but yeah... screen turns off when I put it on my ear(during calls). it allows me to use touchscreen while on calls... but samne doesn't happen when I use apps for audio calling(Skype, viber etc). screen turns off even while using touchscreen. I cant even end my call.
what to do??

 

[xandros9]

To others, does the power button end the call?

I would think its the app just not knowing what to do without the proximity sensor or something.