The most likely cause for this scenario has to do with whether you selected to use the backing folder security when placing the share under governance. That is, if you selected the Use backing folder security for self-service option when placing the share under governance (default), then the backing folder security is used for the share. However, if you cleared the Use backing folder for self-service option when you placed the share under governance, then the share permissions are used for the share.
See the Resolution to determine which permissions are being used.
Use the Object Browser to review the properties for the governed share resource in the QAMDuG table. There should be two entries for the governed share in the QAMDuG table; one entry for the share and one entry for the backing folder.
NOTE: By default, this value is set to True for shares. That is, the Use backing folder security for self-service option was selected when you placed the share under governance. You must clear this option to use the share permissions.