Aria role="heading" and aria-level inside buttons

Hi

I have this markup, and although the validator doesn't show any error, I'd like to know if it would create any problem to users with assistive technologies:

<h1>Main heading</h1>
<button><span role="heading" aria-level="2">Button with heading 2</span></button>
<button><span role="heading" aria-level="3">Button with heading 3</span></button>
<h4>Heading 4</h4>

The validator outline shows that headings 2 and 3 are being skipped.

Any help will be really appreciated.

Thanks.

--
Bernat Lleonart

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