Unable to "Exit Preview" on Block Element

Environment

• OS version: Windows 10
• Browser version: Opera 39
• Extension version: Latest release 2019-4
• Last working version: NA

Steps to reproduce

1. Go to youtube.com
2. Click on "Block Element" from the bubble UI
3. Highlight and click an element to block
4. Click on "Preview" in the filter composer window

Observed behavior

Clicking the "Preview" button on the filter composer window shows a preview of the page but does not show the "Exit Preview" button afterwards

Expected behavior

After previewing a page, the "Preview" button should change to "Exit Preview" to stop the preview of the page

Further information

This is only happening on Opera 39. It does not happen on other versions of Opera or on other browsers.