Pasted content in Pull Requests loses indentation

When copying content that contents indentation into the Description box for creating a Pull request, the indentation will be lost.

For example, by copying the following paragraphs:

This paragraph is indented by 1 space.

   This paragraph is indented by 3 spaces.

      This paragraph is indented by 6 spaces.

Pasting it directly into the description box of in the create Pull request page will result in it appearing like this:

This paragraph is indented by 1 space.

This paragraph is indented by 3 spaces.

This paragraph is indented by 6 spaces.

Note: This doesn't happen with the description box in creating an issue.