If I accidentally R-click while L-click & dragging an object, it vanishes.

I get the context menu, and an apparently empty selection/resize box in the position the object started in. Whatever I do next (Esc, Ctrl-Z, Ctrl-V, click one of the resize handles etc.), the box too then vanishes. Opacity (bottom L) is still 100.

It's so easy to do this, I assume it is a shortcut to some useful (albeit invisible) object state. I've been unable to find a reference to this behaviour so far (me just doing the wrong search?) so I post this 'fix':

In Outline view (View.Display Mode.Outline) the object is still there.
On returning to Normal view (View.Display Mode.Normal) the object is back (phew!).

Seems odd to me that just altering the view resets this. I'm sure there's a simple explanation.

Additional - same happens if you accidentally R-click while L-click/dragging while in Outline view. Return to Normal view, and the object returns.

Right - this freezes the whole canvas, I can't even zoom with the mouse anymore. It gets reset when I zoom with the zoom numbers at the bottom, or switch tools. Please report this at https://inkscape.org/report. On the version that will soon be 1.0, it usually worked, crashed once, and did the mouse-freezing once.