No goals after finishing subgoal

[fpvandoorn]

Prerequisites

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• Reduce the issue to a minimal, self-contained, reproducible test case.
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Description

The following examples shows No Goals on the line after finishing the first subgoal.

example : True ∧ True := by
  constructor
  · trivial

--^ the tactic state shows "No goals" anywhere on this line and the previous line
  trivial

example : True ∧ True := by
  apply id
-- correct goal state at the start of this line (unindented)
  constructor
  · trivial
-- "No goals" at the start of this line (unindented)
  trivial

It should show the same goal state as the following examples

example : True ∧ True := by
  constructor
  · trivial

--^ correct goal state

example : True ∧ True := by
  constructor
  · trivial
  trivial
--^ correct goal state

Note: this seems to only affect subgoals that were proven in one line:

example : True ∧ True := by
  constructor
  · apply id
    trivial
  
--^ correct goal-state
  trivial

Related: #2881

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