Stained Glass Pane recipe only yields 6 panes as opposed to 16

When crafting 6 stained glass of the same color you only get 6 glass panes. Doing so with normal glass yields 16 glass panes.

What I expected to happen was...:
I get 16 glass panes

What actually happened was...:
I got 6 glass panes

Steps to Reproduce:
1. Get 6 stained glass blocks of the same color and 6 normal glass blocks
2. On a crafting table, craft glass panes out of them
3. Notice the different numbers of glass panes you get