wptexturize() #18549 — before and after
These are the shapes the bug touches: a straight quote or apostrophe right after a closing inline tag, which WordPress curls the wrong way. Every line below is typed by hand so it holds still — the before is how a stock install renders it today, the after is how the proposed core fix renders the very same markup. Nothing on this page runs the fix live; it is not in WordPress yet.
Possessives and contractions after a tag
Before (stock WordPress): He‘s here. It‘s fine. Dan‘s truck. rock‘n’roll.
After (with the fix): He’s here. It’s fine. Dan’s truck. rock’n’roll.
Closing quotes after a tag
Before: The word is “quoted“. A possessive after a quoted name: “John”‘s car.
After: The word is “quoted”. A possessive after a quoted name: “John”’s car.
The adjacency guard still works
A space before the quote keeps a normal opening quotation, with or without the fix: He ‘go’ and She said “go” stay open.
The full set of shapes, the bug’s history, and why this belongs in core are in The apostrophe after the tag.