Call screen becomes inaccessible

[mbethke]

Perhaps I'm being thick here but I find it impossible (on every Android version I tried from 5 to 7) to make the call screen reappear when I place a call with CSipSimple and bring any app to the front during the call.This makes it impossible do things like hang up, re-enable a muted microphone etc. Starting the app again brings up the regular UI, not the call.