ExtJS version tested: 4.1.1
Browsers tested: Firefox 18.0.1, Chrome 24.0.1312.56 on MacOS

Related to:
http://www.sencha.com/forum/showthread.php?234813

Description:

When having a form with say 30 or more fields and calling form.Basic.load() to fill it with data, the time it takes for the setValues() call in form.action.Load.onSuccess() is several seconds. My findings regarding the number of calls matches those of user Daniil detailed in the linked post above. And like in the linked post, doing Ext.suspendLayouts() and Ext.resumeLayouts() solves the problem.

The "bug", in my view, is that
Ext.suspendLayouts() and Ext.resumeLayouts() is not used in form.action.Load.onSuccess() or maybe even better in form.Basic.setValues() to avoid this performance issue by default without the developer having to take care of it.