Shuffle + Smart Backspacing = bug

[zzgab]

Description

When Shuffle is on, and Smart Backspace is on, there is a little bug when the program operates the backspacing (it uses the wrong Next String to compute the common part).

See PR #599

Demo

[If possible, include a demo of your issue in a fork of this JSFiddle: https://jsfiddle.net/mattboldt/1xs3LLmL/]

Steps to Reproduce

1. [First Step]
2. [Second Step]
3. [and so on...]

Expected behavior: [What you expect to happen]

Actual behavior: [What actually happens]

Reproduces how often: [What percentage of the time does it reproduce?]

Whenever the natural next string is not the one that the shuffling has picked.