Credit Card Data within Form Validation

[eluser]brightdevice[/eluser]
What kind of security issues are there when using credit cards within Codeigniter's form validation? I'm thinking in terms of re-populating input fields with the submitted credit card data, when there have been errors detected within the form.

I'm aware that when the form is submitted successfully that data can be encrypted and saved to a session database, but I'm not sure how this works with the form validation? Is it generally unsafe to be passing the CC information through that process?

Thanks!