There has always been a problem with Groups and Groupings in Moodle, when the teacher forgets to create groupings for each set of groups. Or, when the teacher forgets to use the groupings in the activity settings.
As everyone using Moodle probably know: When this happen in a course with more than one set of groups, all the groups in all the sets of groups will get the activity, causing confusion at the least and real problems at its worst (for instance with Group Assigments).

• The first step to prevent this would be to have mandatory Groupings, i.e. groupings has to be created first and can then be populated with Groups.
• The second step would be that instead of assigning Groups to activities, one can only assign Groupings. If only a certain group in a grouping should have access to an activity, this would have to be set by Restricted access.

• Also: Since later versions of Moodle also contains "speed group settings" on the course frontpage, the risk to make this mistake have even increased. As a suggestion, the speed settings should only manage Groupings.