WordPress 3.9 doesn’t automatically generate <p> and <br> tag by default

I use WP 3.9 with clean install (not upgrade). And using about two plugins that support 3.9 too (although this is not related to plugin)

When Heading1, Heading2, etc.. are selected it generates <h1>, <h2> tag correctly. But when Paragraph is selected, it doesn’t generate <p> tag. Even when the text was entered, it generates  . (Why not <br> or <p> tag?)

I was reading editor.js when asking this question. Looking for how to make the editor to automatically generates <p> and <br> tag. If anyone want to share the answer here, it would help.

Thanks lots 🙂