some applications have their cache deleted when stopped with ubuntu-app-stop

It seems that some applications have their QML cache wiped by QtMir when they are stopped with ubuntu-app-stop from the command line. So far this seems to include Camera, Gallery and most (but not all) web-apps. Closing the app via the UI maintains the cache.

Steps to reproduce (all from the devices UI or shell):

1.) Open Camera from the Dash/Launcher
2.) ls ~/.cache/QML/Apps
 - Confirm that the Camera app triplet is listed and copy it to the clipboard
3.) ubuntu-app-stop <app triplet from step 2>
4.) ls ~/.cache/QML/Apps

Expected result:

Directory for camera is listed

Actual result:

Directory for camera is not listed. grep'ing ~/.cache/upstart/unity8.log shows "qtmir.applications: Application appId= "com.ubuntu.camera_camera_<version>" Wiping QML Cache"

Camera can be replaced with Gallery or a web-app such as Amazon or Cinco Dias (although Twitter which is also a web-app isn't affected apparently)

$ system-image-cli -i
current build number: 189
device name: krillin
channel: ubuntu-touch/rc-proposed/bq-aquaris.en
last update: 2015-11-26 17:09:32
version version: 189
version ubuntu: 20151126
version device: 20151028-869191d
version custom: 20151111--36-46-vivid