AIR 26/27 iOS app not running in background

In my iOS app I have the uibackgroundmodes set to voip, in the app executeinbackground set to true, and have 2 'timers' which used to run in background fine up to and including AIR 25. In AIR 26/27, when you lose app focus, background activity seems to stop - have an interval and an enter_frame event, not really concerned with the interval, but the enter_frame event was firing just fine on previous AIR versions. When the app has audio playing, when putting it to background it keeps playing (which is good) and the 'timers' keep running, but once the audio stops, so do the 'timers'. I tested with the same code that runs fine in AIR 25 in both AIR 26/27 which do not work.