When I select an FBX to be imported, I check “Import as Skeletal”. When I tick that box, the dialog changes to the one above. As you can see, there is no way to go back to the previous dialog, or untick animation import. The only option is to select a skeleton and import animations, or cancel.
As said, importing works when I delete intermediate files from the project. But after a while the dialog gets broken again.
I am testing importing animations, and am therefore importing, deleting, tweaking in Blender, and re-importing a lot. Could this somehow mess up the editor?