Combination of booktabs and ltablex fails if cell starts with bracket

Question

My document contains several tables, one of which spans several pages. Following this question, I tried to use the ltablex package for that. However, my document doesn't compile anymore if I use that package instead of tabularx.

I was able to isolate the problem. It seems that there's an issue with using the rulers from booktabs in a tabularx environment provided by the ltablex package if the next cell starts with a bracket. Here is a minimal working example that illustrates this:

\documentclass{article}

\usepackage{blindtext}
\usepackage{ltablex}
\usepackage{booktabs}

\begin{document}

    \begin{table}[tbp]
        \begin{tabularx}{\linewidth}{Xr}
            \toprule
            Label       & Estimate \\
            \midrule
            % What follows seems to be the offending line. If I remove 
            % the brackets around `Intercept`, the file is compiled 
            % without an error.
            (Intercept) & 10.0 \\
            \bottomrule
        \end{tabularx}
    \end{table}

    % this is a very big table that spans several pages, which is 
    % why I want to use the `ltablex` package:
    \begin{tabularx}{\linewidth}{Xr}
        \toprule
        Statement  & Number \\
        \midrule
        \blindtext & 1 \\
        \blindtext & 2 \\
        \blindtext & 3 \\
        \blindtext & 4 \\
        \blindtext & 5 \\
        \bottomrule
    \end{tabularx}

\end{document}

Compiling this produces seven errors, most of which are Undefined control sequence \end{tabularx} errors in line 19, i.e. the \end{tabularx} command at the end of the first tabularx environment. Here's the output for the first error (I can post the whole error log if needed):

! Undefined control sequence.
<argument> ...al \expandafter \let \cmrsideswitch 
                                                \@tempa \fi \fi 
l.19             \end{tabularx}

The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

I've found some ways of making the error disappear, but at the cost that the document doesn't contain what I want:

• Remove the brackets around (Intercept) in line 17
• Remove the \midrule command in line 13
• Use tabularx instead of ltablex

So, I have two questions.

1. Is this a bug in one of the packages, or is the bug in my document?
2. How can I fix this without sacrificing the \midrule, the brackets, or the multi-page table?