Why am I unable to automatically apply language suggestions via the Word add-in?

In order to let you automatically apply suggestions, we need to be able to highlight the sentence. In some cases, due to a quirk with MS Word application, our add-in may not be able to always highlight a sentence. As a failsafe, we display a "Copy" button instead of "Accept" in the suggestion card, so you can copy the revised sentence and paste it into your document. 

While we are still investigating the reasons for this, we have observed that this hiccup often occurs in sentences containing non-textual elements like equations. It may also happen if you you are applying suggestions from the add-in with Tracked Changes on. In this case, you can try to force the "Apply" button by switching the Markup options to "Show revisions in balloons"; try collapsing and expanding the same card again to get the "Apply" button.