George Kakosouris

I have noticed a similar (maybe the same) problem as well. Here is how to replicate it:

1. Visit WP-admin > Users.
2. Select a user and click “Edit”.
3. Choose a role from the drop-down menu and click “Update User”. For my tests I chose “Editor”.
4. When the page reloads, scroll down to the “Capabilities” section and click on “Edit”.
5. Asign an additional capability to the user and click “Update”.
6. When the page reloads, visit the user’s edit page once more. The role will be changed.

Cheers