Focus changes after manual selection as the RTE loads
It is been there for years and it's still annoying the hell out of a daily user :)
1. opening up a content element with RTE in it for editing or adding new
2. focusing header field by clicking it
3. start typing
4. realizing you have typed your text into text field not header as it changed the focus as the RTE loads
Solution would be focusing the header or to make it remember it as soon as it's selected, not after the form get's completely loaded.