Line 262 in the file MapServer/php/LoadMap.php reads:
array_push($mapObj->groups, getGroupObject($oMap->getLayer($aLayerIndexes[0])));
The layer that is passed to getGroupObject(..) may or may not be a group layer. In the function getGroupObject(..), group information is queried from this layer through calls such as "$layer->getMetaData('groupLegendLabel')". It seems to me that group information is not returned if the layer is not a group layer. As a result, all metainformation specified for groups in the map file is ignored.
There are a number of solutions to this. One would be to just add a second parameter to the getGroupObject(..) function where the according group layer is passed. Line 262 then could look like this:
array_push($mapObj->groups, getGroupObject($oMap->getLayer($aLayerIndexes[0]), $oMap->getLayerByName($groupName)));
All metadata queries in getGroupObject(..) would then go to the group layer.
