Here, I created the panel with vbox layout and one TextArea item:
Ext.create('Ext.form.Panel', {
width : 400,
height : 300,
layout :
{
type: 'vbox',
align: 'stretch'
},
renderTo : Ext.getBody(),
items :
[{
xtype : 'textareafield',
height : 55
}]
});
After render textareafields height property is equal to 55, but rendered components height isn't equal to 55.
Here is the fiddle: https://fiddle.sencha.com/#view/editor&fiddle/1ulh