Thanks for responding.
I checked the Paint Brush>Project Alpha and it was already unticked.
Just to check Paint Brush, I tried using it instead of the Clone Brush and got the expected results the tutorial showed for using the Paint Brush.
A small clip showing the Paint Brush test:
Just to play around and see if I could trick Clone into working, I tried sourcing the clone from lower/non-pattern layers but output in the pattern layer was still truncated by the current frame of the pattern. I also tried grabbing the content within the pattern frame and moving it across the border, hoping it would allow me to edit the image borders within the confines of a single frame, but placing it across a border just make everything outside of the border cease to exist.