Understood. I appreciate the time you took to analyse the issue. Thanks.

The first signature is a direct key signature (class 0x1f) and this determines the expiration time. The usual case is to have the expiration time in the user id signatures. Our code does not allow to chnage the expiration time of direct key signature. This is because direct key signature are used by PGP and GnuPG only to add designated revokers. Gpg has no means to create a direct key signature like you have in your key.

This is the file I am repeatedly importing in the sessions from my report. It is one of the keys that seem impossible to unexpire for me.
There is no privacy issue: this belongs to a published test suite and is not used by any human.