ntheorem Endmark On Line Alone Doesn't Flush Right

Well, I only have a workaround:

\begin{examplelist}
\NoEndMark % <==========================================================
\item First item would go here.
\item But if there's lots of text in the next item that fills the last 
line in the theorem, ntheorem correctly places the endmark on the 
subsequent line, but it's not flush right. 

\hfill \exampleSymbol % <===============================================
\end{examplelist}

I used \NoEndMark to get no automatik end mark. Then -- important -- I added one blank line and added the wanted end mark manually with \hfill \exampleSymbol.

That is no automatic solution, but you get the end mark at the end of the line and not at the beginning.

With the complete code

\documentclass{book}

\usepackage[T1]{fontenc}
\usepackage{newtxtext}
\usepackage{newtxmath} % requires amsmath

%\usepackage[document]{ragged2e}
\usepackage[amsmath, thmmarks]{ntheorem}
\usepackage[inline]{enumitem}

\newlist{examplelist}{enumerate}{1}
\setlist[examplelist]{label=(\alph*), nosep, wide, labelwidth=!, labelindent=0pt}

\theoremstyle{plain}
\theoremheaderfont{\sffamily\fontseries{bc}\selectfont\normalsize}
\theorembodyfont{\normalfont}
\theoremseparator{}
\theorempreskip{\topsep}
\theorempostskip{\topsep}
\theoremindent0pt
\theoremnumbering{arabic}
\theoremsymbol{$\blacksquare$}
\newtheorem{example}{EXAMPLE}

\begin{document}

\begin{example}

\begin{examplelist}
\NoEndMark % <==========================================================
\item First item would go here.
\item But if there's lots of text in the next item that fills the last 
line in the theorem, ntheorem correctly places the endmark on the 
subsequent line, but it's not flush right. 

\hfill \exampleSymbol % <===============================================
\end{examplelist}

\end{example}

\end{document}

You get the result: