@hugh can you add this to your list? I was able to replicate the problem as stated by RGJ in the OP and also the different behavior as stated in Moin’s reply.
tl;dr the UI behaves differently when searching for “Sign up” (content of the text field) vs “js.sign_up” (name of the text field), then changing the content of the field, then going back to the search.
- expected and correct:
/admin/customize/site_texts?locale=en&q=js.sign_up - unexpected and broken:
/admin/customize/site_texts?locale=en&q=sign%20up