Placing a glass block turns into glowstone

I placed a glass block in my house and it turned to glow stone.

*What I expected to happen was I to be a glass block
I thought it should be see through.

*What actually happened was got a price of glowstone
Describe what happened here

Steps to Reproduce:
1. Place a glass block in an enclosed structure on oak wood
2. Watch it turn to a glowstone block
3. ...