Levels with headings

Hi,

This might be intended, but recently, I've downloaded an epub from Gutenberg.org with the following sequence of headings:

<h2>Text 1</h2>

<h1>Text 2</h1>

<h3>Text 3</h3>
<h3>Text 4</h3>
...
<h3>Text N</h3>

When I create a create a table of contents from all headings, the <h3>-heading of "Text 3" and the <h3>-headings of "Text 4" to "Text N" are placed on different levels (<h3>-headings of "Text 4" to "Text N" are placed as sub-headings of "Text 3"), instead of placing them on the same level as "Text 3".

Regards,

McDummy