Project explorer style changes during runtime.

When I open a project in Qt Creator, the project tree uses nice '>' or 'v' icons to display expanded or collapsed folders.

However after a while it changes to the more classic '+' and '-' icons. There is no hover icon. The selected line background does not change.

I've attached 2 screenshots to make it more clear.

This seems to happen systematically after going back in Edit mode from the QML Designer, but not from the widget designer.

It may also happen at other moments as I remember to have seen this once with a previous version (3.6 I suppose) and I do not usually use the QML designer.