This may be a duplicate, but all the old (fixed) 'MC-4631' and related issues are flooding my search results. After placing and removing lava, I found a single ghost lava block that persisted, made sounds and particles, and added the flame effect but did not burn me when I stepped into it.
Hard to reproduce; suspect a server/client glitch. I think I saw the same with water once, but I wasn't paying proper attention and didn't capture it
