Normally, the user which is the owner of the created workspace is added in the local XWikiAllGroup (workspace members) and explicitly in the local XWikiAdminGroup (local admins) and the initial members are added in the local XWikiAllGroup.
If the workspace name contains an underscore though, like "my_workspace" for example, this is not happening, the all group is empty and so is the admin group.
An immediate result of this is that when the owner of the workspace is accessing the workspace, the workspace information panel asks him to join the workspace since he doesn't find him as member and the initial members are not set. Other side effects might be possible.
To reproduce: create a new workspace using the link in the main home, choose some initial members (different from the owner), membership type doesn't matter but I tried with "Open". In the newly created wiki, go in administration in groups and all groups will be empty.