unknown group name appearing as an access ID!?

i just noticed a new discussion was added on my site and the access level was set to the group level - so that the discussion is only visible to those in the group. for some reason, the name of the group has been set to a name that i don't recognise and that may date back to a very early version of my website. when i create a discussion in the group, i see the correct name of the group appearing in the access dropdown, but a different user sees this 'old' name and i have no idea why. stranger still, when i search the database for the name that is appearing, the name is not found in any tables!

i am using group tools and my own 'containers' plugin, so this is not purely core elgg code, but even so - i have no idea how this is possible!