On 1/26/2020 7:12 AM, between "Wilfred van Velzen : August Abolins":

  AA> Let's see how the signed clear-text behaves.

WvV> This signature was ok...

Thanks for confirming.  That one went out with UTF-8 encoding, but my
own copy (viewing locally) did not verify!  :(

gpg command line and output:
C:\Program Files\gnupg\bin\gpg.exe
gpg: Signature made 01/25/20 21:24:15 Eastern Standard Time
gpg:                using RSA key D0EB2A295204F3167EB2503CEF0E89655789589B
gpg: BAD signature from "August Abolins " [ultimate]


So, it seems that clear-text signing is only gonna work if I avoid UTF-8
charset and stick with ISO 8859-1.

--- Thunderbird 2.0.0.24 (Windows/20100228)