captcha module not working with authenticated users

Hi,

I've installed the 5.x.2 version of the captcha module and the first time I answer correctly the 'math question' in the sitewide contact form, I get an error saying:

"The answer you entered to the captcha challenge is incorrect"

I try a second time and it works. Always works well at the second time. It happens on IE7 and FF.

I've noticed that this only happens with authenticated users. With anonymous users works fine every time.

How can I fix this?

Thanks