When the new "Active Window Details" section of the "Perform a Window Function" window switches to the idle process, the "Size" label will still display the last window's data (all other labels aside from "Process" will be cleared), however clicking it will set the "Resize Window" option to 0 width and 0 height instead.
The "Idle" process can become the active target when using the taskbar to manage windows; One way is to click the "VoiceAttack" entry.
EDIT: Fixed in v1.7.5.13