it's version "2.0-1build2 amd64" installed via apt.
The problem occurs inconsistently (sorry -- I'll add a note about that in the original post) and I don't know what determines if it's going to happen.
I'm on a laptop. I use "CTRL+ALT+left" and "CTRL+ALT+right" to switch workspaces. I have Geany geany-plugin-addons installed and the only enabled plugins are "Addons" and "Lua Script".