I have not been able to determine whether this is one, or two different, bugs - but there is definitely something wrong with Ext.Slider ...
When used with a CardLayout,
1) when the control initializes, something goes wrong if the Slider is not located on the Panel that display initially - the Slider handle becomes offset to the right.
2) when the control value is changed with setValue(), while the parent Panel is not currently visible, the handle positions itself to the far left, regardless of what value you set it to.
I have set up a running example that demonstrates both errors.