Minor Step by Step accordion behaviour inconsistency

[ctorgalson]

See e.g.: https://demo.localgovdrupal.org/births-deaths-marriages-and-citizenship/marriage-and-civil-partnerships/step-by-step/get-married-4

If a user visits the page and manually expands each step, the "Show Summaries" button at top intelligently changes to "Hide Summaries".

The reverse doesn't happen.