Thanks for sharing the issue.
Current workaround for this issue is to use array format for buttons option.
buttons: [{
text: "Apply",
click: function() {
saveInterfaceSettings();
}
},
{
text: 'Cancel',
click: function() {
$( this ).dialog( "close" );
}
}
]
https://jsfiddle.net/y0pvenb4/