Leashing any leashable mob to a fence while holding any placeable block in the offhand slot causes the block to be placed adjacent to the fence that the lead is tied to.
Small bug, but mildly annoying.
Related issues
Comments


Thank you for your report!
We are resolving and linking this ticket forward as a duplicate of MC-298197, as that ticket contains more detailed information and/or has already been triaged by Mojang.
If you would like to add a vote or provide any additional information to the main ticket, it would be appreciated.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support (Technical Issues) – 📧 Microsoft Support (Account Issues)
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki
Unable to reproduce in 1.16-pre2, please check if this is still an issue in 1.16 for you.