Any reason when you add a hidden form field to the form panel that it gets anchor: '100%' ??
I'm using 1.2.2.r48 with a 4.x project.
Perfection as a goal is a nice idea that can point one in a specific direction. However, since "perfection" is an ever changing (evolving?) and moving target, one must admit that perfection can never be obtained...
This is a nice "feature" for all fields when layout is anchor or form and a width is not set on the field it gives it a anchor of 100%. For Hidden it seems weird but this is across all those components that inherit Ext.form.field.Base
Sencha Architect Development Team