Previous seasonal attachments on Season 3 weapons

The seasonal attachments that I have already unlocked are not available on the new weapons in season 3. Instead they are locked to the weapon's mastery level. Is this a glitch or is it intentional? If it is intentional, then I feel like I've been cheated. What was the point of unlocking the seasonal attachments if they won't be available on new weapons going forward until they are unlocked again? DICE, please fix this or give clarification.