Steps to replicate the issue (include links if applicable):

• Get a tour, such as twa1.
• Use gt.definetour and give a button the 'back' action.
• Trigger the tour and try to click on the "back" button.

What happens?:

Nothing, and a console error is logged.

What should have happened instead?:

We correctly go back to the last step.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Wikipedia