When configuring a group, in a group editor specific items are not seen in the list and "Include the children of managed items" is not checked.
In a dashboard set to that group context, the excluded items are seen.
Release :
Component : IM Reporting / Admin / Configuration
If you have a group and subgroup, for example:
group a
subgroup of group a
If you report at the level of "group a", it would contain any items also in "subgroup of group a"