Composer preview ignoring edited filters

Environment

• Browser version: Chrome 83, Opera 69, Firefox 77, haven't tried other browsers/versions
• Extension version: abp-ui-release-2019-4
• Last working version: n/a

Steps to reproduce

1. Go to https://testpages.adblockplus.org/en/filters/image
2. Right click the red square under 'static' section and click on the Block Element from the dropdown menu
3. Composer window will open with suggested filter ||testpages.adblockplus.org/testfiles/image/static/static.png
4. Delete the suggested filter, so that the textarea is empty
5. Click Preview button

Observed behavior

• clicking Preview shows how the page would look like if the filter from step 3 was applied, despite the fact we removed it from the textarea
• text underneath still shows: 1 element(s) selected despite the text area being empty

Expected behavior

• preview should show how the page would look like if the filters, that are currently in the textarea, are applied
• the element(s) selected count should be updated if filters are edited

(I suppose a workaround could be to hide the element(s) selected section and preview button if changes were made to the textarea?)

What to change

• Spec: https://gitlab.com/eyeo/specs/spec/-/merge_requests/341

Further information

• the new UI/UX for the block element was implemented in: https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/761 and https://gitlab.com/eyeo/adblockplus/abpui/adblockplusui/-/issues/638
• note: the same behavior can be observed when adding/editing filters- Preview button always shows the preview as if the initial selection of filters was applied