Joomla! version: 2.5.19
Matukio version: 3.1

Description of my issue:
I just installed 3.1 on my test environment and did some testing:
Using the Google Recaptcha on the frontend, I can enter a wrong string into the field and the subscription to the event will be accepted.

I tested three times.
1. I changed just the last digit of the first string. Subscription accepted.
2. I put a random sting in. Subscription not accepted
3. I change just the last digit of the first sting. Subscription accepted.

In case of not accepted, the subscription form restarts again. This is definitively user unfriendly.