Workspace Algebra Hidden Workspace Deleted

[cailafinn]

Describe the bug Running a script from the algebra docs causes this error to appear:

Unlocking __python_binary_op_single_value
Error occurred in handler:
Traceback (most recent call last):
  File "/Applications/MantidWorkbenchNightly.app/Contents/Resources/lib/python3.8/site-packages/mantidqt/widgets/observers/ads_observer.py", line 23, in wrapper
    func(*args, **kwargs)
  File "/Applications/MantidWorkbenchNightly.app/Contents/Resources/lib/python3.8/site-packages/mantidqt/widgets/observers/ads_observer.py", line 60, in deleteHandle
    self.presenter.close(name)
  File "/Applications/MantidWorkbenchNightly.app/Contents/Resources/lib/python3.8/site-packages/mantidqt/widgets/observers/observing_presenter.py", line 32, in close
    if self.current_workspace_equals(workspace_name):
  File "/Applications/MantidWorkbenchNightly.app/Contents/Resources/lib/python3.8/site-packages/mantidqt/widgets/observers/observing_presenter.py", line 50, in current_workspace_equals
    return self.model.workspace_equals(name)
  File "/Applications/MantidWorkbenchNightly.app/Contents/Resources/lib/python3.8/site-packages/mantidqt/widgets/workspacedisplay/table/model.py", line 151, in workspace_equals
    return self.ws.name() == workspace_name
RuntimeError: Variable invalidated, data has been deleted.

To Reproduce Run this script:

w1 = mtd['workspace1']
w2 = mtd['workspace2']

# Sum the two workspaces and place the output into a third
w3 = w1 + w2

# Multiply the new workspace by 2 and place the output into a new workspace
w4 = w3 * 2

Expected behavior No error should appear.

[jhaigh0]

When I run the script, is says workspace1 doesn't exist, which I think makes sense? I loaded two workspaces and tried the rest of the script with them, and it worked with no errors. Maybe I'm misunderstanding the issue.

[sf1919]

@cailafinn and @jhaigh0 is this still an issue?