What problem does this address?

When block patterns have a padding set with a CSS selector, the preview may not be rendered properly because of missing classes.

Example:

In this example, the block should get a padding set by the following CSS in the theme

:is(.wp-block-group, .wp-block-cover).alignfull {
	padding-block: var(--wp--preset--spacing--90);
}

Here's the expected preview:

To get the expected preview, the outer block should have the alignfull class.

What is your proposed solution?

The outer block should get its alignment class and custom class. Ok

Edit: custom CSS classes are added to the outer block, only the alignment class is missing