" when I click on the font which ether deletes the line or adds one"
Technically, attributes such as underlining, bold, color, etc. are considered formatting not fonts. A pre-defined combination that includes more than one formatting attribute (e.g. bold and red and underlined) is called a style.
It's possible that you somehow applied a style to your document or section of your document.
Does this happen in all documents or are you having problems with just one document?
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