Hi,

thanks for getting back to me. Yes, yesterday evening I could successfully send a captcha again. Empty / incorrect submissions were mistakes on my behalf. My Browser saves a history of entered solutions and automatically takes completions out of it - for example, if one captcha requires the phrase "dogecoins" and one requires only "dogecoin", it automatically selects "dogecoins" as a completion for "dogecoin".
Since Mybitmine.co is pinned in my browser, there may be some times where the page was loaded (after I started the browser and opened another site) but left unused until the session timed out.
Also, when refreshing the browser window, POST data will be resent. Doing this after solving a captcha might result in both "premature" and potentially incorrect submissions as you observed them. Just a suggestion.
A jQuery/AJAX based submission would be a solution to that, as in a traditional form submission (a submit button) the entire site would have to be reloaded - this would allow to avoid the resending of POST data and reduce traffic load on all sides. On the other hand, you'd exclude older browsers - IE6 and the likes of it - but who wants them, anyway?

Regards

thelinuxist