Basically, the screenshot explains the problem: any click in any filed of the form opens the previous build results. I cannot fill out the form when it is open from the "Pull Requests" tab:

In addition to this issue, if I press "Rerun" button anywhere, a build either won't start at all, or starts with the default parameters (like when it was triggered by GitHub) and does not display the form.

All of this together makes using the UI nearly impossible