ToggleButton when toggled creates a strange dark square around the text
The black square remains even after toggling to the off state, and persists until restarted. The button's toggled state is also a strange colour.
The text of disabled buttons also look strange (not clean), but I cannot tell if this is how they were planned to look or not.
toggled to ON state:
The toggle button is "M", Disabled button is "next node", and the finally the "delete" button is a button in its normal state.

Here is the application after toggling to OFF state:

+1 for disabled button text.
To reproduce:
OSX 10.9,
add simpleButton.setEnabled(false); as line 91 into ButtonDemo.java
btw. in IDEA disabled buttons are ok.
I fixed this issue in PR #13.
I have a fork with this and other fixes/improvements at AlexFalappa/Darcula