IGMP needed on PIM Interface towards source

Hi

I have read and seen that when you enable pim sparse mode on an interface it is enabling IGMP automatically.

I have an irb interface that faces only towards a source.

I am seeing PIM state created on that interface for the required groups.

But I am seeing log entries for:

Interface irb.123: Group record with invalid mode for SSM group

Thus my question is do I have to have IGMP in this scenario where there are no recievers on that interface?

thanks