Spell check unexpected behaviour for first word in heading

spell check will not replace the first word in a heading.

Please resubmit this bug report and make sure that: 1) you follow the bug report template, 2) you use the default theme (no css) and 3) there are no third-party plugins enabled (You can use the sandbox vault for 2 and 3).

Attach a screen recording of this happening in the sandbox vault.