First seen on the WMF internal office wiki, and then confirmed on mw.o. This is a pretty serious problem for me, because important changes were made to pages without my being made aware of them.
I am watching a page. Someone makes a minor edit to the page. It shows up in my watchlist, but (correctly) does not light up the toolbar, nor does it generate an email. Then the same person makes a non-minor edit to the same page. It correctly shows up in my watchlist, and incorrectly does not light up the toolbar (nor does it send email). Additional non-minor edits continue to not generate notifications.
I don't know if the behavior would be the same if 2 different people made edits, first minor then not.
Example edits can be seen here: