Unable to hang up outgoing call

[Tobias Stollenwerk]

When I make an outgoing call, I am unable to hang up. I can do so only by changing to another app and then return to the dialer-ap.

Step to reproduce:

1.) Open the dialer-app
2.) Start an outgoing call
3.) Try to hang up by pushing the hang-up button

Then the hang-up button is unresponsive.

Further steps to workaround

4.) Swipe from the right and switch to another application
5.) A green panel appears on the top of the screen.
6.) Click the green panel to return to the call
7.) Now the hang up button works and you an hang up the call

My System is the following: (I will translate some descriptions from german):
- Hardware: BQ Aquaris 4.5 Ubuntu Version

From Settings->Device Information-> Operating System :
- OS-Build Number: OTA-8.5
- Ubuntu-Image-Part: 20151210
- Ubuntu-Build-Description: Ubuntu 15.04 -armhf (20151210-005527)
- Device-Image-Part: 20150821-736d127
- Device-Builde-Description: KRILIN01A-S15A_BQ_L100EN_2028_151210
- Adaption-Image-Part: 20151111--36-46-vivid

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Tiago Salem Herrmann (tiagosh)]

dialer-app only update existing calls in the live call screen when it is in foreground. (we unregister the telepathy observer when it's in background to avoid other problems).
If you lock the device with dialer-app open, then unlock it, it is still reported as inactive by Qt.application.active.
If we try to make a call in this state, the app won't be able to control it. (including the hangup button not working)
Once we swipe the app to background and then foreground again it works again, and Qt.application.active reports the right state.

Did we land any change to the dialer-app focus logic on unity recently?