If the Apply changes window is too low when you open the mini-form, the mini-form will be offscreen.

[DrewNaylor]

Workaround: Closing the mini-form with Esc/Escape then switching back to the Apply changes window, maximizing it, and opening the mini-form or moving the Apply changes window up enough will bring the mini-form onscreen. A real solution would be to just put the controls in a sidebar for the Apply changes window, which ~~may~~ will be done in a future version.