Hi Gumbanomicon,
thanks for bringing that up again. I also forgot about it. I tried to reproduce the bug. I copied a skill in the database and then changed it icon and some parameters and texts. Then I added a node with this new skill to a skilltree. After saving everything and closing and reopening the game the skill icon was shown properly.
It seems that this is more of a RPG Maker issue. Did you restart the game properly after copying the skill? To apply changes to the database you need to properly save the project and then close the game and reopen it by using play test. Can you try that and check if the bug still happens?
Best regards,
Felski