I don't understand. Are the less-than and greater-than < > signs visible in the To field and in the address book?

Yes they all are. As I understand it, only the outer ones should be there and the quote marks shouldn't be there either.

Quote marks usually mean the entry has a space in it. Often caused by a leading or trailing space from copy and paste of the email in the first place. After you have a space, all bets are off as to what messes up in the formatting.

Thanks Matt for the reply. I checked the format of the address very carefully and there are no spaces in it, leading, trailing, or otherwise.

Do you have an email from that specific address in your Thunderbird? First check the header of that email that the star beside the name is coloured yellow. If not the address in your address book is different in some way. (in case you did not know clicking those stars open address book entries for coloured ones and adds the outline star entries to the address book.)

Second.

delete the entry from your address book and then start a new message for that address. does Thunderbird still offer it in the suggestions? If so it is also in another address book, like collected addresses.