problem with UTF-8 in carddav

I am trying to set up thunderbird on linux mint, to use contacts from my mailbox.org. It works, but there are no polish characters. When I export single contact from mailbox web client, I see for example this text:

BEGIN:VCARD

VERSION:3.0

N;CHARSET=UTF-8;ENCODING=QUOTED-PRINTABLE:Ba=C5=BCy=C5=84ski;Jan

So, there is no 'Bażyński Jan', as it should be in UTF-8, instead there is a quoted-printable version which at this point is a legacy form, should not be used in vcard 3.0. Mail client doesn't interpret this values and lists 'a=C5=BCy=C5=84ski' instead of 'Bażyński'

Is there a fix for that problem? Is there any way to set up mailbox.org server to use plain UTF-8?