Minor UI bug on admin panel / themes editing pages

I’m currently just seven commits behind latest on 2.9.0.beta3 ( 98f3349c31 )

A new bug has appeared when customising themes via admin control panel (I’m almost sure it didn’t used to do this last month) whereby I am being prompted to save or discard my changes even when I have no made any changes.

Steps to repro:

  1. Go to Admin > Customize > Themes > Light > Edit CSS/HTML
  2. Click on any tab, in this example, the Body tab
  3. Click inside the text box to place the cursor - as if you were about to add/edit something:

  1. Click on the word Light (as if about to switch themes and edit a different one):

  • Expected behaviour:
    – I have not made any changes so I should be returned to the previous /admin/customize/themes/2 page

  • Actual behaviour:
    – I am prompted and asked if I want stay or discard my changes and move on (but I have made no changes):

I’ve done some further testing, this might only be an issue if you have edited the defaults previously.

For example:

The blue Save button at the bottom appears to become immediately active, again though I have made no changes.