Form doubles itself after clicking "Get my invite" inside Slack form


I found strange bug here, inside Slack Invite plugin. The form just doubles itself (one is placed below another) after I submit email address (it doesn’t matter if email really exists or not, is user already the part of Slack group or not, etc.). I’m using latest Quark Open Publishing theme and latest Form plugin.

Problem solved. I find out that page must have “default” as page template and not the “form”.