Setting the UseStrictHeaderRule in content.ini to false does not apply to headers in custom tags. In other words, the header within a custom tag always needs to be one level lower than the last header tag before the custom tag.

Steps to reproduce

Although the UseStrictHeaderRule setting has been set to false in the override content.ini, the following input does not seem to get stored as intended in the XML-block of an article:

<header level="1">header 1</header>
<header level="2">header 2</header>
<custom name="somecustomtag"><header level="1">header 1</header></custom>

After storing the article as a draft, the content is stored as follows:

<header level="1">header 1</header>
<header level="2">header 2</header>
<custom name="somecustomtag"></custom>

<header level="1">header 1</header>

Whereas the following will be stored correctly:

<header level="1">header 1</header>
<header level="2">header 2</header>
<custom name="somecustomtag">
<header level="3">header 3</header>
</custom>

This is with the online editor disabled. The UseStrictHeaderRule seems to be picked up correctly.