What I expected to happen was for the button to stay disabled as it is, therefore, causing the world to never be created.
What actually happened was that the button got re-enabled.
Steps To Reproduce: 1. Click on "Singleplayer". 2. Click on "Create New World". 3. Remove the entire world name from the box, so that the button "Create New World" gets disabled. 4. Resize the window.
Environment
Windows 8.1 and Java Version 8 Update 51 / Update 60 / Update 66 / Update 72 / Update 74 / Update 77
Confirmed.
If pressed, the world is created with the name
World