By completely I mean that it retains it for the first letter only. So to illustrate what I mean, follow these steps:
create a text field, doesn't matter if it's a Heading, paragraph or whatever type.
Edit the text to have the entire line turn bold.
Duplicate the element.
Edit that duplicated item by highlighting the entire text within it.
Start typing replacement text.
My results were that the first letter was Bold and everything after that was normal. As any other text editor would do, it should retain that setting for everything typed when it's text being "replaced". If the text were "deleted" and then you typed, then the Bold setting might make sense that nothing was bolded, but it does still bold the first letter even when deleting the text. Either way is fine for the deleting text (bold or normal as long as the entire text is one or the other), but when you're just overwriting text it should all retain the Bold setting for everything you type. That is the "typical" way a text editor works anyways. Either way there's a glitch in that it's retaining a setting for only 1 character.
NOTE: I've also just discovered that ....
If you do not delete or overwrite the very first character of the text line, then it will keep the bold settings for the rest of the line that you type. But of course, you still have to go back and delete the first character lol. Just thought I'd let you know that I just did this accidentally and found that out. So... Bold works as it should as long as you don't delete the first character. Hope that helps some in working out what the issue is. :)