Conversion from Classic to Blocks: caption shortcode fails to convert correctly

[afercia]

Tested with the captioned image shortcode from the themes unit test data:

[caption id="attachment_754" align="alignnone" width="604"]<a href="http://build.wordpress-develop.test/wp-content/uploads/2011/07/100_5478.jpg"><img class="wp-image-754 size-large" src="http://build.wordpress-develop.test/wp-content/uploads/2011/07/100_5478.jpg?w=604" alt="Bell on Wharf" width="604" height="453" /></a> Bell on wharf in San Francisco[/caption]

• open a post with the content above in Gutenberg (adjust the attachment ID if needed)
• content is in a Classic block, as expected:

• in the Classic block "More Options" menu, click "Convert to Blocks"
• the captioned image gets converted to an Image block with two images: the second image is within the caption:

Code after conversion:

<!-- wp:image {"id":754,"align":"none"} -->
<figure class="wp-block-image alignnone"><a href="http://build.wordpress-develop.test/wp-content/uploads/2011/07/100_5478.jpg"><img src="http://build.wordpress-develop.test/wp-content/uploads/2011/07/100_5478.jpg?w=604" alt="Bell on Wharf" class="wp-image-754"/></a><figcaption><a href="http://build.wordpress-develop.test/wp-content/uploads/2011/07/100_5478.jpg"><img class="wp-image-754 size-large" src="http://build.wordpress-develop.test/wp-content/uploads/2011/07/100_5478.jpg?w=604" alt="Bell on Wharf" width="604" height="453" /></a> Bell on wharf in San Francisco</figcaption></figure>
<!-- /wp:image -->