The 'want_' API for BIER has a handful of issues:

1. on simple consistency, it takes enable_disable when other 'want_*' APIs take enable
2. if you ask for stats you're already receiving it returns an error - other APIs accept the command without argument
3. The state for a connection ID remains even when the connection ID is terminated (which is, in fact, common to all the want_* APIs, though it's a bug).  Combined with (1) this means you can ask for IGMP updates on a fresh connection and then receive an error because they're turned on - even though they shouldn't be.