I think the "Invisible-ness" from spectator stayed with me when I when back to creative
It should make you not invisible when going back to creative

I don't know what really happened. I've never seen it before
I was on a small smp server, went over to my friend's base to help him with something, I had to go, but I wanted to be back at my base. I /gamemode sp-ed and then /tp-ed to my base, I went in my base, and then I did /gamemode c, I was puting my stuff away when i realized that, in my inventory, I was invisable (a picture of yourself is in your inventory), but with no effects I drank milk, but it didn't do anything

Steps to Reproduce:
1. Spectator
2. /tp
3. Creative