When I tried to mirror the right side of the stomp walk to the left, I first deleted the left sides keyframes. To my surprise, when I hit the play button, the animation still ran as if I hadn't deleted any of the keys on the left side! I tried undoing and deleting them again from both the graph editor and dope sheet, but it had the same effect. How do I delete the keyframes on the left side to that when I play the animation, the left side stays still an only the right side moves?
Just make sure you are selecting all the controls you want to remove the animation from - and also make sure you are 'deleting' the animation.
By default the mouse will pop over the "clean keyframes" option when you hit x or delete.
(Cleaning the keyframes doesn't delete the animation, it just deletes the unnecessary keys)
If that doesn't solve your issue, can you post a video of the steps you are taking.
Here is my video of what is going on:
https://vimeo.com/1032836930?share=copy#t=0
Interesting Andrew.
I would need to look at your file to be sure but perhaps you have some animation in the NLA which is overriding the active action.
But can you post your file somewhere where I can look at it.
Dropbox or similar.
Or you could even use one of the exercise submissions that has the submission type set to "file" rather than video.
That way I can download it.