around 3 years ago i have started a topic for customized icons (https://www.giuspen.com/topic/optimized-toolbar-icons/)
What i found out during adapting to my own icons is, that some stuff is coming from/through the system. In particular your mentioned icons like open and save, seem to not be maintained by Cherrytree itself. So i believe if these do not match, then they might be not as accurate delivered by the system. What’s your running OS?