App crashes when using StyledItem + Ubuntu.Layouts

This is something that I've seen often while testing Ubuntu Document Viewer on desktop.

*** Using Document Viewer:

1) Launch DocViewer
2) Open a LibreOffice presentation document
3) A sidebar with the list of slides is placed at the left of the window
4) Resize the window so that its width is less than units.gu(120)
5) The list of slides is now visible at the bottom of the window
6) If the app hasn't crashed yet, resize the window so that: width > units.gu(120)
7) Repeat 3, 4, 5, 6.

- What happens?
DocViewer crash.

*** Using the minimal example below:

1) Launch the .qml file
2) A blue rectangle is visible on the screen
3) On a phone: rotate the screen to landscape (from portrait)
     On a desktop: resize the window so that height > width
4) On a phone: rotate back to portrait
     On a desktop: resize the window so that width > height

 - What should happen?
The rectangle becomes yellow.

- What happens?
On the phone: the rectangle is still blue. A black surface becomes visible on the bottom. The app has crashed.
On the desktop: the app crashes.

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Tested on a BQ E5, with rc-proposed (r302)
Tested on desktop, vivid+overlay, UITK version: 1.3.1872+201602271301-staging-0+1.3.1795+16.04.20160106~ubuntu15.04.1