** This is a notebook with custom styles, but the same happens with the default notebook.
** Pasting text into MyInfo from word has similar problems (cannot change the style of a lot of the pasted text)
You can find the steps to replicate this in the attached image.
The latest build adds a Clear All style item in the Styles drop box. You need to use it when you want to completely remove the formatting of a text instead of just changing the paragraph formatting of it. You can refer to the documentation about the difference between Normal style and Clear All.