Only N-1 icons appear in dock when reversing "Workspaces" defaults

[Bob Lawrence]

When the defaults are left in the "Workspaces" preferences, everything functions as expected. But when the options are reversed from the defaults, the result is that the icon for the most recently opened app on a workspace is missing from the dock.

Steps to reproduce:
Select "Dock Preferences" -> "Workspaces"
For "Pinned application dock icons" select "Display on all workspaces"
For "Unpinned application dock icons" select "Display unpinned apps only from current workspace"
Apply the settings

Now open any app (like calculator). The app opens on the current workspace, but its icon does not show in the dock. Now open another app (like font viewer). It too opens on the current workspace but without its icon appearing in the dock. However, the icon for the first app (calculator) now shows in the dock. Repeating for a third app has the same results (its icon is missing from the dock), but now both the first and second apps appear in the dock (calculator and font viewer).

This behavior continues with each new app opened. The most recently opened app on the workspace is not displayed in the dock. Only n-1 app icons on the current workspace are displayed. Switching to another workspace and back will momentarily bring all app icons into the dock for that workspace, but then the unexpected behavior continues when further apps are opened. Setting the "Workspaces" preferences back to default restores expected (but not desired) behavior.

This behavior was observed on an Ubuntu Mate 18.04.2 LTS system with Mate Dock Applet 0.87 (GTK3)