Heading bb-code does not round-trip as expected

[Xon]

If you enter the bb-code;
Code:

[B][HEADING=1]1[/HEADING][/B]

And then toggle bb-code mode on & off, this causes a newline to be inserted before the heading. This is because of the following HTML being generated;
Code:

<p><strong><h2>1</h2><p></strong></p>

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