Node Teaser Makes Editing a Node report processed content after saving...

I'm a bit of a newbie so bear with me :)

When I enable Node Teaser, create a node (with or without teaser), save it, view it. Looks great.
Go back to edit it and the body box contains the processed html (with
etc) rather than the pre-input filter body.
If I disable Node Filter this is not the case.

Steps to reproduce:

1. Create Node
2. Set Input Format to Full HTML
3. Enter the following in the Body box

First Line of <b>Text</b>

Second Line of Text

Third Line of Text

6. Save the Node
7. Edit the Node.
8. See that the Body box now contains

<p>First Line of <b>Text</b></p>
<p>Second Line of Text</p>
<p>Third Line of Text</p>

If I disable Node Teaser this the body still contains the entered body without the <p></p> etc like so:

First Line of <b>Text</b>

Second Line of Text

Third Line of Text

I think this should be the preferred option since all of the other modules work like this, therefore I presume it's a bug in Node Teaser causing it to change the content of the body unnecessarily.

Feel free to contact me if you need any more information.