Hi, this is how it looks like when you create tileset in way you create standard resources, which is wrong. You need to create new scene with tiles as objects and then convert this scene to tileset.
Here is video showing how to do it correctly:
Based on image you showing us, you are using 3.0.6 Stable. Just tested on my Ubuntu laptop. Everything is as excepted, you just created tileset in wrong way, it does not work like standard resources.