When you are adding a new system definition details for a data collection group, the UI picker is a bit clunky to work with if you want to add or remove multiple mib groups.
What would make this ui action in the snmp mib compiler easier is Vaadin's Twin Column Select (TwinColSelect).
5.15.6. Twin Column Selection with TwinColSelect
This way it would also enforce uniqueness in that you can only add an entry once to the mib group list.