receiving notifications for replies to someone else

### Steps to reproduce

I have a test server on a subdomain of my main domain, so `@hhl:domain.tld` and `@hhl:sub.domain.tld`.

Usually I'd suspect fallbacks being the issue, but I don't see that here?

### Outcome

#### What did you expect?
notify only the OP

#### What happened instead?
Getting replied to `@hhl:domain.tld`, I now also receive notifications for it on `@hhl:sub.domain.tld`.
The event content is
```json
"body": "> <@hhl:domain.tld> message\n\nreply",
"format": "org.matrix.custom.html",
"formatted_body": "

In reply to @hhl:domain.tld
message

### Operating system

arch

### Browser information

Vivaldi 4.3.2439.41 (Official Build) snapshot (64-bit)

### URL for webapp

develop.element.io

### Homeserver

sub.domain.tld

### Will you send logs?

No