When showing an email with a broken signature (our mailing list server adds some lines to the contents of mails, such that the original signature does not match anymore), KMail displays:
```
Not enough information to check signature validity.
```

When clicking "Show Details", it displays:
```
Message was signed with unknown key <Key ID>. 
The validity of the signature cannot be verified. 
Status: Bad signature
```

This feels wrong.  I would expect KMail to display "Bad signature" instead of "Not enough information to check signature validity.".

Further, for an email that contains another email (forwarded as attachment) that was signed with the same key, whose signature matches, KMail displays this correctly:
```
Message was signed by <Email Address> (Key ID: <Key ID>). 
The signature is valid and the key is fully trusted.
```

Thus the key obviously is not "unknown" as KMail displays for the outer email.

A more graphical explanation of the problem:
---
| <Outer Email Header>
| ---
| Not enough information to check signature validity. -- Show Details
| ---
| | Encapsulated message
| | <Inner Email Header>
| | ---
| | Signed by <Two Email Addresses>. -- Show Details
| | ---
| | <Inner Email Body>
| ---
---

After clicking "Show Details":
---
| <Outer Email Header>
| ---
| Message was signed with unknown key <Key ID>.
| The validity of the signature cannot be verified.
| Status: Bad signature
| ---
| | Encapsulated message
| | <Inner Email Header>
| | ---
| | Message was signed by <One Of The Two Email Addresses Only> (Key ID: <Key ID>).
| | The signature is valid and the key is fully trusted.
| | ---
| | <Inner Email Body>
| ---
---

(<Key ID> is the same in all cases.)

I am using KMail 5.6.3 on KDE neon User LTS 5.8.