TinyMCE will convert accents to HTML entities like:
à becomes á
So you see the problem there, you search in your database for "á" or even "a" (in case you are using unaccent), and you get nothing.
In my case, I was using full text search in Postgres, using the dictionary portuguese_unaccent (custom dictionary check here).
So keep in mind you can always make TinyMCE not convert stuff: