In the new New UI experience a site admin (non-space admin) is allowed to add users to a space using the Share button. This can potentially cause confusion   because, by default, a non-space admin is not allowed to provide space permissions to other users. However, without any warnings, a site admin (who is not space admin) is able to provide space permissions to other users by using the new Share feature.
 
Given the following scenario: 

• Dummy User A  is NOT a space admin but has space permissions on a space
• Dummy User B is a user who does NOT have any access/space permissions on the space
• Dummy User A shares a page with Dummy User B

Outcomes:

1. If Dummy User A a is NOT a site admin >> Dummy User A will NOT be able to add Dummy User B to the space permissions when sharing the page
2. If Dummy User A a is a site admin >> Dummy User A will be able to add Dummy User B to the space permissions when sharing the page.