When you add a chevron upgrade it isn't removed from your inventory and when you destroy the stargate you get the upgrade back giving you a second one. I just did this to make sure it wasn't lag and I've gotten 3 upgrades from it.

Just tested in survival, and it correctly takes my chevron item during upgrade. HOWEVER, if I am in Create Mode, mine acts as you are describing. Returning the upgrade on block destruction has always been so, and I assume to be a feature, not a bug?

This is working as intended if you're in creative mode. If you use the configurator then this is also expected.