Hello,
Thank you for contacting our Help Desk. This is not a bug, the dummies are working as intended. You can only gain 30% of your current skill level, such as novice, apprentice, regular, and so on until Transcender. You only gain skill exp from using skills on a dummy. Auto attacks do not give any skill experience. Once your current points go above 30% of the required points to rank up, you will stop getting any skill experience. At class rank 10 you will be able to gain 100% of your skill level off of dummies with the last 70% being at a decreased rate. This is also required in order to gain skill points at Transcender rank, all of which are at the decreased rate. You must have Platinum service or a Blessing Bead Plus active to see any of these effects.
If you have any other questions please contact us again.