Gold Pickaxe not working correctly

I was using my gold pickaxe to breakdown my beacon so I can move the location, but I noticed the game didn't give me the diamond blocks back. At first I thought the game might be lagging so I broke a few more to realize I lost 9 blocks of diamonds. I then tried the pickaxe on blocks of iron and the same thing happened. I have no screen shot cause I don't want to keep wasting blocks.