Same thing happen in Grammarly. In this case I tested against Reinli Stave Church which has a text "…who is buried beneath the south-east entrance" in the fourth paragraph. The term "south-east" should be written "southeast".
Before correcting the term is
<g class="gr_ gr_38 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling multiReplace" id="38" data-gr-id="38">south-east</g>
afterwards it is just southeast, that is the enclosing tag is removed.
I guess this change happen without any of the tracked events, probably with a direct change of the dom. For a few years there has been available Mutation event types.
MutationObserver is not yet supported in all of our target browsers, although these days it is just down to IE10 and some fairly old versions of FF/Chrome. For that reason we don't fully support browser plugins that modify the DOM.
We do however have a surface observer that polls the DOM node where the cursor currently is (to support the browser's built in spellchecker), so if you place your cursor before using the plugin the change should be observed.