This bug allows you to go through the world border in snapshot 16w44a (and maybe later) which is kinda a return of a earlier bug in 2014. It applies to X and Z axis.
MC-119389
World Border Bug (16w44a)
Resolved
Invalid
0
Thank you for your report!
However, this issue is Invalid.
Your Minecraft version is outdated. We currently take issues for version 1.12.
Please update to the latest version as it includes the newest fixes. If you still have this problem after updating, then please create a new issue.
In case of a game crash, please also attach the crashlog.
Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – 📖 Game Wiki