javascript error when updating out of date themes after import

Hi Team. Here’s a rare bug.

Steps to reproduce:

  1. Open the Themes page in an org with out of date themes.
  2. Import a custom theme.
  3. Click the ‘update out of date themes’ button and continue.
Expected Result:
All themes are updated, including newly imported theme.

Actual Result:
Page hangs with blocked ui due to javascript exception.

Reload the page between steps 2 and 3.