Quick scrolling through timeline with m.notice messages causes some of them to suck surrounding regular messages into themselves

[rom4nik]

Steps to reproduce

1. Join a room with one or more m.notice messages present, such as #ping:maunium.net
2. Send a regular text message (or have another user send it, as was the case in screenshots below)
3. Scroll quickly through older messages in the room, making use of inertial scrolling
4. After a few attempts one or more m.notice messages will pull one of regular messages into its body, rendered as if they were part of the same message bubble
5. Long press the m.notice part of bubble and go to source - you'll see source of m.notice message
6. Long press the regular message's text on the bubble and go to source - you'll see source of the regular message

This issue can be reproduced in other rooms too, but in the ping room it's easier to spot due to large amount of m.notices. It's been a problem on older app versions too, definitely on 1.5.32.

Outcome

What did you expect?

m.notices not sucking nearby regular messages into themselves.

What happened instead?

One of m.notices as displayed in timeline after a few seconds of scrolling up and down:

The "Pong! (...)" response was sent by Ping [nevarro.space], "hyper test" was sent by "Hyperbot" in response to my "test" message.

Menu and message source after long press on "hyper test" text:

Menu and message source after long press on "Pong! (..)" text:

Your phone model

Google Pixel 3

Operating system version

Android 12

Application version and app store

Element 1.6.0 from .apk in GH releases

Homeserver

Synapse 1.83.0

Will you send logs?

Yes

Are you willing to provide a PR?

No

[rom4nik]

Rage shake sent for a similar case, this time messages from daedric were rendered with nearby m.notices sent by pong bots:

[rom4nik]

I've noticed that this issue occurs only if rich text editor is enabled in Labs on EA versions >= 1.5.24.

[rom4nik]

This issue was introduced in 00f9c36 (#8011).