Search is broken after message edits

[rda0]

Description

I was pointed here from this Element issue: element-hq/element-web#27386

This happens on matrix.org using app.element.io and on our self-hosted instance.
It happens in encrypted and unencrypted rooms.

Steps to reproduce

Steps to reproduce (using Element (Desktop/Web) v1.11.65)

1. Create a new room
2. Send message: foo
3. Send message: bar
4. Search for foo or bar works ✔️
5. Edit the bar message: bar -> foo

Outcome

What did you expect?

6. Search for foo shows 2 foo results
7. Search for bar shows nothing (I think I would not expect to find the original message before the edit)

What happened instead?

6. Search for foo: shows nothing (No more results)
7. Search for bar: shows 2(1) foo result (I think it only finds 1 message and the other is shown as surrounding text)

Homeserver

matrix.org, phys.ethz.ch

Synapse Version

1.105.1

Installation Method

pip (from PyPI)

Database

PostgreSQL

Workers

Multiple workers

Platform

Debian 12 VM

Configuration

none

Relevant log output

exmaple.com:443 1.2.3.4 - - [24/Apr/2024:13:00:10 +0200] "POST /_matrix/client/v3/search HTTP/2.0" 200 78 305 0.017 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:125.0) Gecko/20100101 Firefox/125.0" TLSv1.3 TLS_AES_128_GCM_SHA256

### Anything else that would be useful to know?

_No response_

[rda0]

Similar but different: #8686

[reivilibre]

Seems like it could probably be the same as #8686 indeed but I'm also not sure, so will leave this here.