Buttons without selected state with Breeze-theme on KDE

If you are using a recent KDE version, e.g. with openSuSE Leap 42.2, you will notice that some toolbar buttons don't show a selected (or toggled) state.

You can fix (or work-around) it, by opening the System Settings and selecting ‘Application Style’ in the ‘Appearance’ section. On the tab ‘GNOME Application Style (GTK)’ you can find the options for selecting GTK themes:

If you select, e.g. ‘Adwaita’, and click ‘Apply’, SmartGit's toolbar buttons will show their selected (or toggled) state: