"Preformatted names" strategy thinks single letter words are not valid

The SlugEntityNameValidation aka "Preformatted names" page naming strategy thinks that several single letters (at least three) connected by hyphens do not form a valid page name, despite of generating such names itself.

To reproduce, activate that page naming strategy in the wiki admin, and set  both "Transform names automatically" and "Validate names before saving" to "Enabled".

Then try to create a page with name "a b c". An error message appears that this is not a valid page name.