Roman numerals in TOC are not in smallcaps - microtype problem with memoir

Question

I'm using the memoir class for typesetting a book. In the \frontmatter I have a chapter with a section and a subsection.

My problem is that, in the TOC, the page number of the chapter appears in lowercase, and I would like it to be in smallcaps (as they appear in the section and subsection):

Even stranger, when I tried an MWE, the problem didn't appear:

\documentclass[a5paper, 11pt]{memoir}
\usepackage[utf8]{inputenc}
\usepackage[spanish,es-tabla]{babel}
\usepackage[sc]{mathpazo}
\usepackage{biolinum}
\usepackage{eulervm} 
\usepackage[T1]{fontenc}

\chapterstyle{dash}
\pagestyle{ruled}
\settocdepth{subsection}

\begin{document}

\frontmatter

\tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents* 

\chapter{A modo de introducción}    
\section{Convenciones}    
\subsection{Números de línea}

\mainmatter

\chapter{Cecilia Payne, PhD.}
\chapter{Antonia Maury, Aydte.}

\end{document}

Edit:

I think I found the package responsible for the behaviour: microtype:

\documentclass[a5paper, 11pt]{memoir}
\usepackage[utf8]{inputenc}
\usepackage[spanish,es-tabla]{babel}
\usepackage[sc]{mathpazo}
\usepackage{biolinum}
\usepackage{eulervm} 
\usepackage[T1]{fontenc}

\usepackage{microtype} % <--- This is the problem

\begin{document}

\frontmatter

\tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents* 

\chapter{A modo de introducción}
\section{Convenciones}
\subsection{Números de línea}

\mainmatter

\chapter{Cecilia Payne, PhD.}
\chapter{Antonia Maury, Aydte.}

\end{document}

I would like the xi appear as XI.

Edit 2:

After the wonderful answer and insight of Iacobus1983, I think that the problem is far out of reach. So I think that I will get the chapter titles and numbers in small caps:

\documentclass[a5paper, 11pt]{memoir}
\usepackage[utf8]{inputenc}
\usepackage[spanish,es-tabla]{babel}
\usepackage[sc]{mathpazo}
\usepackage{biolinum}
\usepackage{eulervm} 
\usepackage[T1]{fontenc}
\usepackage{microtype}

\settocdepth{subsection}
\renewcommand*{\cftchapterfont}{\scshape}
\renewcommand{\cftchapterpagefont}{\scshape}

\begin{document}

\frontmatter

\tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents*
\cleardoublepage \tableofcontents* 

\chapter{A modo de introducción}

\section{Convenciones}

\subsection{Números de línea}

\mainmatter

\chapter{Cecilia Payne, PhD.}
\section{Una sección}
\subsection{Una subsección}

\chapter{Antonia Maury, Aydte.}

\end{document}

It doesn't look bad. ;)

Answer 1

Since the issue happens only in the Table of contents (not in other small caps text within the document), you can (with memoir) just add \scshape in the page number font, so:

\renewcommand{\cftchapterpagefont}{\scshape}

If I add this to your preamble I get this (I've added a section and a subsection to ensure that everything is ok):