When two different Rich Text fields are displayed in two panels,
and the keyboard focus is on a heading line in the first panel,
then clicking in the second panel on a heading’s expand/collapse icon
causes both headings in both panels to toggle their state.
It also happens if you first click anywhere in right panel (moving the keyboard focus there), then click the expand/collapse icon on a heading there, then click anywhere back in the other Rich Text (where the cursor was left on a heading).
(NOTE: the left panel below shows an entity, and the right shows a Document, though they look similar)