Journal notes formatting selected text

I'm having some issues formatting selected text while I'm editing a journal note. Often when I select some text and try to apply formatting to it, such as Header 1, Header 2, etc., it not only changes the selected text, but nearby text as well. This is especially noticeable inside table cells, where it usually is applying the formatting to the entire cell contents instead of just the selected text.

The "styles" in the dropdown are all block elements. Header 1 is, literally <h1>. They're not something that you use to change the appearance of a word in the middle of a sentence. It's also worth mentioning that the rich text box used is from a third party; they made the decision to wrap the entire paragraph in <h1> when you click Heading 1, instead of only applying it to the selected text (which would then turn one line into three, if you selected a piece of text in the middle of a line). Except quote, for some reason. I don't pretend to have an ear to the wall of the design meeting for the tool. ;)