Using Undo after using Composer caused me to lose work

How to reproduce:

  1. I used Composer to move some inline styles to a new css file (cool!) and then made several additional changes manually.
  2. I did Command + Z several times to refer to a previous version of code. I undid enough steps that it deleted the new css file Composer had created (no big deal)
  3. HOWEVER Upon deleting that css file, Command + Shift + Z no longer works. I can no longer redo my changes, which means I lost not only the refactor but also the manual work I had done.