unknown critical bit

[ilf]

With current GnuPG, I get an error with a specific key:

% gpg --version
gpg (GnuPG) 2.1.19
libgcrypt 1.7.6
<snip>

% mkdir test; cd test # new empty GnuPG homedir

% gpg --homedir=. --recv 631EFC0642A8D5D22C52FBA0E62E990F36377134
gpg: keybox '/home/user/test/pubring.kbx' created
gpg: assuming bad signature from key E62E990F36377134 due to an unknown critical bit
gpg: assuming bad signature from key E62E990F36377134 due to an unknown critical bit
gpg: /home/user/test/trustdb.gpg: trustdb created
gpg: key E62E990F36377134: public key "Dan Blah Meredith (This is my current primary key. This replaces my old key ID 1024D/0x9C1BDFB4.)" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg:               imported: 1

% gpg --homedir=. --recv 631EFC0642A8D5D22C52FBA0E62E990F36377134
gpg: WARNING: unsafe permissions on homedir '/home/user/bar'
gpg: assuming bad signature from key E62E990F36377134 due to an unknown critical bit
gpg: assuming bad signature from key E62E990F36377134 due to an unknown critical bit
gpg: key E62E990F36377134: "Dan Blah Meredith (This is my current primary key. This replaces my old key ID 1024D/0x9C1BDFB4.)" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1

% gpg --export-options export-minimal --export 631EFC0642A8D5D22C52FBA0E62E990F36377134 | pgpdump | grep critical | sort | uniq -c
     10         Hashed Sub: features(sub 30)(critical)(1 bytes)
     11         Hashed Sub: key expiration time(sub 9)(critical)(4 bytes)
     11         Hashed Sub: key flags(sub 27)(critical)(1 bytes)
     11         Hashed Sub: signature creation time(sub 2)(critical)(4 bytes)

The "critical" bit is defined in
https://tools.ietf.org/html/rfc4880#section-5.2.3.1

In GnuPG, this is caused in
https://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=blob;f=g10/sig-check.c;hb=refs/heads/master#l473

But both my OpenPGP *and* GnuPG skills fail me at that point.

Can someone help me understand why this is failing?

Thanks!

-- 
ilf

Über 80 Millionen Deutsche benutzen keine Konsole. Klick dich nicht weg!
		-- Eine Initiative des Bundesamtes für Tastaturbenutzung
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