When you add a block to a region in a layout, it comes up with a modal form titled "Add block" with a text field labeled "Search" and a list of available blocks. That search form has never worked in any sense for me. I found the original issue, https://github.com/backdrop/backdrop-issues/issues/929, but it looks and behaves nothing like that. I'm using Chrome. Does this work for other people? I don't see any Javascript console errors, only a Deprecation warning about some code in jquery.js.

Accepted answer

When I want to test something like this, I spin up a sandbox site using the "Demo Backdrop" option on the front page of BackdropCMS.org - https://backdropcms.org/demo/create

This is a great way to check to see if problems on my local site are also effecting a clean version of Backdrop CMS core. 

I tested this in a Sandbox and it seems to work fine. I use this feature a lot and don't recall ever having any problems. 

Just to be sure, is this what you are talking about:

Comments

When I want to test something like this, I spin up a sandbox site using the "Demo Backdrop" option on the front page of BackdropCMS.org - https://backdropcms.org/demo/create

This is a great way to check to see if problems on my local site are also effecting a clean version of Backdrop CMS core. 

I tested this in a Sandbox and it seems to work fine. I use this feature a lot and don't recall ever having any problems. 

Just to be sure, is this what you are talking about:

Yes, that's it. Well, hmm. It literally has never worked for me. The sandbox works in the same browser, so it's not browser extensions. I guess creating a fresh copy locally is the next step.

Thanks

It's a bug in the Form Element Layout module, turns out - it was writing a set of classes without checking if some already existed.