Incorrect Grouping for Multi-Value Columns

When grouping by a column that contains a list with multiple values, the grouping behaves incorrectly.
Instead of duplicating the record into each relevant group, the system creates expanded or nested group combinations.

Incorrect behavior:

Group Value1
- item 1
Group Value2
- item 2
Group Value2 Value1
- item 3

Expected behavior:

Each item should appear in all groups that correspond to its list values:

Group Value1
- item 1
- item 3
Group Value2
- item 2
- item 3

In other words, an entry with multiple values in the grouping column should be included in every applicable group, not placed into combined or nested groups.