Yai, it wurks!! [\:D/] Thanks a lot for fixing that! [:D]

I just re-checked the grouping/ungrouping thingy and found out that the problem only occurs if I change the group's name before un-grouping it (when I make a "tree" from a brown pipe and a greenish blob, it should at least have a proper name, not just "group -2-" [;)] ). The "stem" loses its brown colour, and the top loses its plant texture, resulting in a shiny metal... lollipop [:p]
So it seems that when changing a group's attributes, individual attributes are overwritten.