It appears that decorators are not automatically updated on style changes. If you set a decorator and change the font-size, or the font, or any other property impacting layout, then the fallback decorators do not update properly.
Original:
After adding some paragraph spacing:
Resizing the window also brings strange results, with what appears to be an incorrect offset.
I will have to come back to this for read-aloud in the foreseeable future, but this is an issue one should be aware of.