PWAE sometimes highlights items in email messages I'm reading, which is obviously not needed.
A (maybe related?) issue is that from time to time the highlight marks will remain on the screen after the message is no longer open. I haven't seen this behavior with emails that I'm composing (or in other apps, for that matter, not that I've tested that much). The only way to clear the highlights is to quit PWAE. Quitting Mail does not clear them from the screen.
Another issue I've only noticed in Mac Mail: if you click on an item, but don't select the suggestion (just click elsewhere in the Mail window to dismiss the PWA popup), all highlights disappear until you start typing again. I cannot reproduce this behavior in other apps (e.g. TextEdit). In other apps, the highlights remain when you click to dismiss the popup.
And finally, a feature request: would it be possible for PWAE to ignore quoted text when replying to an email? Not a huge deal, but a tad distracting to have highlights popping up in the quoted text. Additionally, the errors in the quoted text prevent the PWA icon from ever showing green.