Hello David,
by default WPM records only web-page related events. Custom keystrokes are not in this category. However, you can use "XY capture mode" (Edit->Toggle XY Capture mode). When you enable it, WPM records all keyboard events as well as most of mouse events. Give it a try.
Just keep in mind that this mode does not have awareness of the page itself, it really records exact inputs and uses exact coordinates instead of HTML element-based navigation. You should use it only for specific actions and rest of your recording should use normal mode if possible.