org-sort has an optional argument with-case. By default its sorting ignores
the case. When org-sort is called within a table, it calls
org-table-sort-line with the argument. org-table-sort-line defines a let
variable sort-fold-case (not with-case) but fails to use either variable
when sorting and always sorts with case.

This is with the very latest org:
Org mode version 9.1.13 (9.1.13-elpa @
/Users/helehvas/.emacs.d/elpa/org-20180702/)

     -Heikki

Heikki Lehväslaiho - skype:heikki_lehvaslaiho cell: +358 40 850 6640
http://about.me/heikki