In the Online Editor, if you create a custom tag with a header at the top, and there is a header one level lower as the first element above the custom tag, the custom tag breaks (in other words, you lose the custom tag element).

Steps to reproduce:

1. Create or edit an article;
2. Add a paragraph to "body" field e.g. "Heading 1";
3. Set it with a "Heading 1" style;
4. Click on "Insert custom tag" button and add a factbox;
5. Set the text inside the factbox with a "Heading 2" style;
6. Disable text editor, and verify the resulting code is OK:

<header level="1">Heading 1</header>
<custom name="factbox" custom:title="factbox" custom:align="right">
  <header level="2">factbox</header>
</custom>

7. Re-enable editor;
8. Highlight first paragraph and set it with a different style e.g. Heading 3;
9. Disable editor, and check the resulting code. The custom tag is gone:

<header level="3">Heading 1</header>
<header level="2">factbox</header>