in the second post i found a workaround that works well also in the previus version of IE.
Just adding my name to the list:
Originally Posted by caballero
With ExtJS 4.2.1, I'm still getting auto-width QuickTips cut off with Mac OSX Firefox, even when using the "delete Ext.tip.Tip.prototype.minWidth;" workaround.
Tooltip still cuts off content in IE9
The problem is fixed in IE 10 but still visible in IE 9,
Is There a fix for IE 9?