Users belonging to a group already invited in a share site cannot be individually invited, to overwrite the group's role setting an individual role.
How to reproduce?
1) in Explorer, as 'admin', create three users 'user1', 'user2', 'user3'
2) in Explorer, as 'admin', create a group 'group1'
3) in Explorer, as 'admin', add 'user1' and 'user2' to 'group1'
4) in Share, as 'admin' create a site 'site1' (private)
5) in Share invite 'group1' as 'consumer' (see screen shot 1_group1_consumer.png)
6) in Share invite 'user1' as 'collaborator'
It is not possible to do step 6) as the Add button is grayed out (see screen shot 2_user_cannotbeinvited.png). Only users not in the group can be invited (e.g. 'user3')
One would expect to be able to overload the permissions of the group by tuning the role of individual users in the group, in the same way this is done in Explorer. Indeed, consider the following 'explorer only' scenario:
1) as admin create two users 'user1' and 'user2'
2) as admin create a group 'group1' and add user1 and user2 to group1
3) as admin create a folder 'folder1' under company home
4) in folder1's permissions: untick Inherit Parent Space Permissions
5) invite group1 as consumer
6) invite user1 as coordinator (screen shot 3_permissions.png)
7) log in a user2: check he has a consumer role (screen shot 4_user1.png)
8) log in a user1: check he has a coordinator role (screen shot 4_user2.png)
In conclusion the behaviour of Share and Explorer is not consistent.