The rendered attribute is used to control whether a widget is rendered on the
page as well as whether it should be included in processing the postback. This
in itself is not a problem (except that the word rendered is misleading to
users), however the value of rendered is revaluated when the form is submitted,
and this value is used to decide whether to process the component.
Unfortunately, there is no easy way around this, especially if we move towards a
more stateless lifecycle. This may be a simple matter of better educating users.