When smoke from a campfire that starts disappearing is in front of smoke from another campfire that isn't disappearing yet, the smoke that is not disappearing is not rendered behind the disappearing smoke and so you can see whatever is behind both smokes even though you shouldn't be able to.
Thank you for your report!
We're tracking this issue in MC-161898, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki