Apologies for the title of this issue, blame it on whoever chose the semantics for this part of Moodle
Basically this is fairly simple: When no group or grouping exists, the [Not in a grouping] grouping (in the left multi-select box) is selected by default, with 0 in brackets. If a new grouping is created and a group is created within that new grouping, the number of groups reported within the [Not in a grouping] grouping also increases.
Another needed improvement is to allow new groups to be created in the [Not in a grouping] grouping. This is important for such cases as an accidental deletion of an imported group, which currently must be assigned to a grouping if re-created.