this seems to be bug in import, please report into the public issue tracker at support.dnnsoftware.com.
As a workaround, you may use a modified version of AddFolderPermission stored procedure by executing the following code in Settings > SQL window of the PersonaBar:
IF EXISTS (SELECT * FROM sys.Procedures WHERE object_id = OBJECT_ID(N'{databaseOwner}[{objectQualifier}AddFolderPermission]'))
DROP PROCEDURE {databaseOwner}[{objectQualifier}AddFolderPermission]
GO
CREATE PROCEDURE {databaseOwner}[{objectQualifier}AddFolderPermission]
@FolderID Int, -- not Null!
@PermissionID Int, -- not Null!
@RoleID Int, -- might be negative for virtual roles
@AllowAccess Bit, -- false: deny, true: grant
@UserID Int, -- -1 is replaced by Null
@CreatedByUserID Int -- -1 is replaced by Null
AS
DECLARE @ID Int;
BEGIN
SET NoCount ON;
MERGE INTO {databaseOwner}[{objectQualifier}FolderPermission] AS T
USING (SELECT @FolderID AS FolderID,
@PermissionID AS PermissionID,
CASE WHEN IsNull(@UserID, -1) != -1 AND @RoleID = -1 THEN Null ELSE @RoleID END AS RoleID,
@AllowAccess AS AllowAccess,
NullIf(@UserID, -1) AS UserID,
NullIf(@CreatedByUserID, -1) AS CreatedByUserID,
GetDate() AS CreatedOnDate
) AS S ON T.FolderID = S.FolderID AND T.PermissionID = S.PermissionID AND IsNull(T.RoleID, -1) = IsNull(S.RoleID, -1) AND IsNull(T.UserID, -1) = IsNull(S.UserID, -1)
WHEN MATCHED THEN UPDATE
SET @ID = T.FolderPermissionID,
T.AllowAccess = S.AllowAccess,
T.LastModifiedByUserID = CASE WHEN T.AllowAccess = S.AllowAccess THEN T.LastModifiedByUserID ELSE S.CreatedByUserID END,
T.LastModifiedOnDate = CASE WHEN T.AllowAccess = S.AllowAccess THEN T.LastModifiedOnDate ELSE S.CreatedOnDate END
WHEN NOT MATCHED THEN INSERT
( [FolderID],
[PermissionID],
[RoleID],
[UserID],
[AllowAccess],
[CreatedByUserID],
[CreatedOnDate],
[LastModifiedByUserID],
[LastModifiedOnDate]
) VALUES
( S.FolderID,
S.PermissionID,
S.RoleID,
S.UserID,
S.AllowAccess,
S.CreatedByUserID,
S.CreatedOnDate,
S.CreatedByUserID,
S.CreatedOnDate
);
SELECT IsNull(@ID, SCOPE_IDENTITY());
SET NoCount OFF;
END; -- Procedure
GO