I installed Optimizely Forms into Alloy Sample. I added default captchar element to a certain form container. I got invalid message at captchar control when I click Submit button at first time even I filled correct text. But it works at second time. I thought it is bug but it is not after I have digged into code.

And here is the thing that I found: Session is using for validating captchar. It means the captchar validator will return false if Captchar Session is expired or you do not enable Session in your app.

Hope guys won't be suprised if you see something like this one day :)