Cannot set trust on one identity

[Andrew Gallagher]

I appear to have an ID on my longstanding key that I can't set to 
ultimate trust. I had this issue on my previous macbook, and after 
migrating to a new one the problem persists:


```

gpg> trust
pub  rsa4096/0xFB73E21AF1163937
      created: 2013-07-02  expires: 2022-12-09  usage: SCA
      trust: ultimate      validity: ultimate
ssb  rsa4096/0x6B09069314549D4B
      created: 2013-07-02  expires: 2022-12-09  usage: E
      card-no: 0005 00002ED9
ssb  rsa4096/0x5C1EC404D5906629
      created: 2015-04-26  expires: 2022-12-09  usage: S
      card-no: 0005 00002ED9
ssb  rsa4096/0x85FDF561DA8C0C46
      created: 2015-04-26  expires: 2022-12-09  usage: A
      card-no: 0005 00002ED9
[ultimate] (1). Andrew Gallagher <andrewg at andrewg.com>
[ultimate] (2)  Andrew Gallagher <andrewg at llagher.net>
[ultimate] (3)  Andrew Gallagher <ab.gallagher at gmail.com>
[ultimate] (4)  Andrew Gallagher <andrew.gallagher at siren.solutions>
[ unknown] (5)* Andrew Gallagher <andrew.gallagher at siren.io>

Please decide how far you trust this user to correctly verify other 
users' keys
(by looking at passports, checking fingerprints from different sources, 
etc.)

   1 = I don't know or won't say
   2 = I do NOT trust
   3 = I trust marginally
   4 = I trust fully
   5 = I trust ultimately
   m = back to the main menu

Your decision? 5
Do you really want to set this key to ultimate trust? (y/N) y

pub  rsa4096/0xFB73E21AF1163937
      created: 2013-07-02  expires: 2022-12-09  usage: SCA
      trust: ultimate      validity: ultimate
ssb  rsa4096/0x6B09069314549D4B
      created: 2013-07-02  expires: 2022-12-09  usage: E
      card-no: 0005 00002ED9
ssb  rsa4096/0x5C1EC404D5906629
      created: 2015-04-26  expires: 2022-12-09  usage: S
      card-no: 0005 00002ED9
ssb  rsa4096/0x85FDF561DA8C0C46
      created: 2015-04-26  expires: 2022-12-09  usage: A
      card-no: 0005 00002ED9
[ultimate] (1). Andrew Gallagher <andrewg at andrewg.com>
[ultimate] (2)  Andrew Gallagher <andrewg at llagher.net>
[ultimate] (3)  Andrew Gallagher <ab.gallagher at gmail.com>
[ultimate] (4)  Andrew Gallagher <andrew.gallagher at siren.solutions>
[ unknown] (5)* Andrew Gallagher <andrew.gallagher at siren.io>

gpg>

```


I appreciate that I can probably fix this by purging and reloading the 
key from a portable copy, but I'm curious what's going on here, as it 
appears to be a problem with this particular kbx/trustdb...


```

gpg (GnuPG/MacGPG2) 2.2.24
libgcrypt 1.8.7
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
<https://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Home: /Users/andrewg/.gnupg
Supported algorithms:
Pubkey: RSA, ELG, DSA, ECDH, ECDSA, EDDSA
Cipher: IDEA, 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH,
         CAMELLIA128, CAMELLIA192, CAMELLIA256
Hash: SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB, BZIP2

```


A