"Not enough space in inventory" for hotbar after a Khitan Tile was in the hotbar

Game mode: [Online | PvE | official Server]
Problem: [Bug]
Region: [EU]

So, I had some Khitan Building Tiles in my inventory. I the last tiles I had in my hotbar were the Foundations.
Now I have one slot free in the hotbar and whenever I want to move something into it I get the message “Not enough space in inventory”.

Here’s an example of what I mean:

Relogging didn’t help, so I decided to remove my bracelet, since it should free up the hotbar completely.
And voila…a random Khitan Table outa nowhere.

Steps on how to reproduce issue: