Taking flag in creative

What I expected to happen was...:
When clicking middle mouse while in creative minecraft gives you that block you're looking at ,clicking at flag should give same flag

What actually happened was...:
I get black empty flag instead

Steps to Reproduce:
1. Create a custom flag
2. Place it
3. Click middle mouse button while in creative on flag
4. ???
5. You get black flag (not profit 😞 )