Memoir class and Turkish Characters in Header

Question

I want to use the Memoir class based template offered by gablin presented here.

I am using Turkish babel package. There is a problem with one Turkish character in heading that is İ (dotted I). If the character İ is the first letter, there is no problem as seen following.

But if the İ is not the first letter, it is seen as I (not dotted). For example:

The following is what I want:

How can I fix this issue?

MWE:

\documentclass[a4paper, 11pt, twoside, openright, turkish]{memoir}

\RequirePackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[style=numeric-comp,sortcites=true]{biblatex}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[oldstylenums]{kpfonts}
\usepackage{microtype}
\usepackage{textcase}
\usepackage[inline]{enumitem}
\usepackage{xspace}
\usepackage{graphicx}
\usepackage{ifthen}
\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{pifont}
\usepackage{array}
%\usepackage{varioref}
\usepackage{lettrine}
\usepackage{lipsum}
\usepackage{relsize}
\usepackage{svn-multi}
\usepackage{siunitx}
\usepackage[bottom]{footmisc}
\usepackage{xstring}
\usepackage{multirow}
\usepackage{datetime}
\usepackage{etoolbox}
\usepackage{ragged2e}
\usepackage{nicefrac}
\usepackage{listings}
\usepackage[rgb,hyperref]{xcolor}
% Load hyperref package last
\usepackage{hyperref}


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%    DOCUMENT CUSTOMIZATIONS
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% Set left and right margins to equal ratio
\setlrmargins{*}{*}{1}
\checkandfixthelayout

% Customize heading appearances
% Define styles
\newcommand{\partSize}{\Huge}
\newcommand{\partStyle}{\lsstyle\scshape}
\newlength{\partNumSizePt}
\setlength{\partNumSizePt}{60pt}
\newlength{\chapterNumSizePt}
\setlength{\chapterNumSizePt}{60pt}
\newcommand{\partNumSize}{%
  \fontsize{\partNumSizePt}{1.2\partNumSizePt}\selectfont%
}
\newcommand{\partNumStyle}{\partChapterNumColor}

% Customize parts
\renewcommand{\partnamefont}{\partSize\partStyle}
\renewcommand{\partnumfont}{\partNumSize\partNumStyle}
\renewcommand{\printpartname}{}
\renewcommand{\printparttitle}[1]{%
  \normalfont\normalcolor\partnamefont #1
}

\makeatother
% Define colors
\newcommand{\titleColor}{\color[rgb]{0.616, 0.0627, 0.176}}
\newcommand{\partChapterNumColor}{\titleColor}

\begin{document}
\part{Koordinat Sistemleri}
\end{document}