Attention to the JTextField, the left border is a little thicker.
And this is what it looks like on another PC with the same project
It doesn't looks like a code problem, yet I can't tell why.
The environment is both under JDK 1.8.0-31, Windows10 Build 10586, eclipse Mars. It was normal on mine two days ago, but it do happened without any change of code. And it works well if I run it with the exported jar file...