Impossible to remove workspace for module that no longer exists

I have the following workspaces open:

[mcatanzaro@victory-road gnome-build-meta]$ bst workspace list
workspaces:
- element: apps/libgnome-games-support.bst
  directory: /home/mcatanzaro/Projects/libgnome-games-support
- element: core-deps/glib.bst
  directory: /home/mcatanzaro/Projects/glib
- element: core/epiphany.bst
  directory: /home/mcatanzaro/Projects/epiphany
- element: core/glib-networking.bst
  directory: /home/mcatanzaro/Projects/glib-networking

I want to remove the workspace for core/glib-networking.bst because I deleted that element, replacing it with core-deps/glib-networking.bst. But it's not possible:

$ bst workspace close core/glib-networking.bst
[--:--:--] START   Loading pipeline
[00:00:00] FAILURE Loading pipeline
Error loading pipeline: Could not find file at /home/mcatanzaro/Projects/gnome-build-meta/elements/core/glib-networking.bst

To close the workspace, it seems I first have to revert the commit that removed the element, then close the workspace, then undo the revert. It would be nice if that was not required.