When starting an app in landscape a black bar is temporarily down the right side

When starting an app in landscape a black bar is temporarily down the right side, the left side appears to be about the width of the display if the app was launched in portrait mode. Which suggests the app might always be launched with portrait widths and then not resized until the app is active?

What happened:
1) Start an app, such as System Settings
2) Rotate the device so that the app is landscape mode
3) Keep the device in landscape and launch the messaging app from the launcher
4) A black box appears on the right side of the app while starting up (it is white/same colour as the left side for some apps but you can still see the header resizing)

What I expected to happen:
At step 4 for the app to be launched with the correct width.

Note this was found while having the 'hack' to have the unity8-dash in landscape mode, so happens a lot easier as you can launch apps in landscape mode from the dash. The 'hack' involves editing the /usr/share/applications/unity8-dash.desktop file and commenting/removing the line "X-Ubuntu-Supported-Orientations=primary" and then restarting unity8.

$ system-image-cli -i
current build number: 245
device name: mako
channel: ubuntu-touch/rc-proposed/bq-aquaris.en
last update: 2016-02-21 16:46:13
version version: 245
version ubuntu: 20160220
version device: 20160112
version custom: 20160201-5-vivid