problem listing role members for db_ssisltduser and db_ssisoperator roles using sp_helprolemember

I was trying to find out the role members for db_ssisltduser and db_ssisoperator roles. But the results from the GUI and from sp_helprolemember are different.

From the GUI (msdb -> Security -> Roles -> Database Roles) double click on db_ssisltduser. It shows 4 members (dc_admin, dc_operator, dc_proxy, MS_DataColletorInternalUser)

But when I run EXEC sp_helprolemember 'db_ssisltduser', it only returned 2 members (dc_operator, dc_proxy)

so I run is_rolemember on the 2 missing members

select is_rolemember('db_ssisltduser', 'MS_DataCollectorInternalUser')

select is_rolemember('db_ssisltduser', 'dc_admin')

and they both return 1, that means they are the members for db_ssisltduser role.

Same problem with members for db_ssisoperator role

From GUI, it shows 4 members (dc_admin, dc_operator, dc_proxy, MS_DataColletorInternalUser)

EXEC sp_helprolemember 'db_ssisltduser' only show 3 members (dc_operator, dc_proxy, MS_DataColletorInternalUser)

Does anyone have idea why sp_helprolemember doesn't return all the members for a role?

I had tried this on my MSSQL 2008 and MSSQL 2012. I was login using the "sa" account.

Any help will be appreciated! Thanks!