In the editor, when adding one block that has validation errors, the global warning for the post shows up immediately upon saving, but the warning for the specific block does not:

However, upon hovering over the offending block then the warning immediately pops into view:

It seems that the change to the store did not get propagated to the block, so it takes another mutation to the block (e.g. selecting it) to cause it to see the changes.

This likewise happens when the validation error has been fixed. Upon saving the post, the warning sticks around until the block is interacted with again:

Upon hovering over the toolbar, the warning then disappears: