"Jiggling" the resizable out of bounds is fixed , but part of the issue remains:
  • When resizing horizontally, vertical boundingbox is not honored.
  • When resizing verti.., vice versa ^

Problem easily spottable via running:

PHP Code:
var div document.createElement('div');
div.id='myDiv';
div.setAttribute('style','background:#ff0;width:500px;height:300px;');

var 
img document.createElement('img');
img.id='myImg';
img.src='grass.jpg';
div.appendChild(img);

document.body.appendChild(div);

Ext.create('Ext.resizer.Resizer', {
    
target'myImg',
    
preserveRatiotrue,
    
constrainTo'myDiv'
}); 
on http://dev.sencha.com/deploy/ext-4.0...zer/basic.html

Dragging horizontally or vertically will make the resizable break-out of the "other" constraint.