reCaptcha and Kindle Fire HD

Could somebody explain if and how reCaptcha works on Apple and Android devices (e.g. iPad, Kindle Fire, etc.)? I use reCaptcha to ensure that e-mail messages sent to the Web Master and other Society Management members are only sent by "humans". I've only got a Kindle Fire HD (plus Windows PC) and when I try testing on the Kindle, everything works until I press the "Submit/Send" button. Then, there's a pause with a circling "wheel" next to the button, the screen clears and I'm left with a message "Your session has expired. Refresh the screen to Continue" (these words are from memory and may not exactly reflect the error message but they are pretty close.) The web site is running under Joomla 3.4. Many thanks. David -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.