When I pass my cursor over a paragraph, a triangle-shape appears at the left side of the text. This just started as far as I can tell.

If I then click on a paragraph, it makes it so I can NOT use the enter button (say to add another paragraph above or below this one), until I 'reformat' the paragraph and apply the 'normal' style to it (which was applied before I click on the paragraph with this 'odd' cursor).

!!! IMPORTANT -- I just noticed that if I do click on a paragraph, the Heading 3 style / formatting is automatically applied - but I DO NOT WANT THIS, and have never activated this, as far as I know???

What's going on, and how can I stop this?