Deskbar Systray wrong orientation when "Arrange items in a single row" is checked

When using the panel in Deskbar mode, in the Status Tray, Notifiers and Icons are put in separate boxes, and thus on separate lines.

Shown: Workspace Switcher, PulseAudio plugin (first two icons), Status Tray (First two Notifier icons, then five Icon icons on two lines), then the Keyboard Layout and the Power Plugin on one line.

This is a bit messy. It would be nice to improve this by putting all the Status Tray Icons in the same box, so they pack together on as few lines as possible. Ticking "Arrange items in a single row" sort of does this.

However, this arranges them in the wrong direction.

For bonus points, it'd be nice to be able to optionally attach other plugins to the Status Tray, for better packing.