Put a player unit in the editor, start it, and run this code in the console:
```
group0 = createGroup [WEST, false];
group1 = createGroup [WEST, false];
_flag = isGroupDeletedWhenEmpty group0;
group0 deleteGroupWhenEmpty false;
group0 createUnit [typeof player, getpos player, [], 5, "NONE"];
group0 createUnit [typeof player, getpos player, [], 5, "NONE"];
(units group0) join group1;
[_flag, isNull group0]
```
The code returns [false, true], meaning that the group is deleted, despite the 'delete when empty' flag returning false.