Earlier today, the Growth team deployed structured mentor list to all Wikimedia wikis. This switched mentor list from a wikitext page to MediaWiki:GrowthMentors.json, edited by mentors (non-admins) via special pages and the action=growthmanagementorlist API.
While we did test how blocks interact with the new feature, we only tested the user interface, and not the API. Today, I noticed that while the special pages do ensure the user is not blocked, the API (action=growthmanagementorlist) does not. This means blocked users are able to enroll as mentors via action=growthmanagementorlist, or to edit any of their mentorship-related properties.
Successfully reproduced at test.wikipedia.org. I'll suppress the edits and block entries for security.