When pasting formatted text from a text editor such as Notepad++ and/or Sublime text editors into the description using the Visual Editor the following may happen:

Anything starting with a Tab will be duplicated and line end/return will be ignored
Pre paste:

     hello
world.
isn't this
a beautiful day?

Post paste:

hello helloworld.isn't this a beautiful day?

Anything starting with a special character will be duplicated and line end/return will be ignored
Pre Paste:

<random>
    <more>
        <text>

Post paste:

<random><random> <more> <text>

Using the Text editor does not cause this issue, only the visual editor.

Work around:

Right click near the cursor, paste your formatted text.

OR

Use the Text editor to paste formatted text will also semi-respect and maintain the format.