Unwanted extra spaces are included before and after backslashes in biblatex URL

I have a biblatex reference with a URL field. However, every backslash is surrounded by spaces.

I am using

\usepackage[sorting=nyt, citestyle=authoryear, bibstyle=authoryear, isbn=false, firstinits=true, url=false, terseinits=true, dashed=false, maxcitenames=3, maxbibnames=99, backref=true, doi=false]{biblatex}


What causes this, and how can I remove them?

EDIT: MWE

My biblatex .bib file is this:

@ONLINE{Soderberg2010,
author = {Soderberg, T},
title = {Section 5.1: The origin of the {NMR} signal.},
year = {2010},
url = {http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/Chapter__5%3A_Structure_Determination_II/Section_5.1%3A_The_origin_of_the_NMR_signal},
urldate = {2013-5-16}
}


This works:

\documentclass[11pt]{amsart}
\usepackage{geometry}                % See geometry.pdf to learn the layout options. There are lots.
\geometry{letterpaper}                   % ... or a4paper or a5paper or ...
%\geometry{landscape}                % Activate for for rotated page geometry
%\usepackage[parfill]{parskip}    % Activate to begin paragraphs with an empty line rather than an indent
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{epstopdf}
\DeclareGraphicsRule{.tif}{png}{.png}{convert #1 dirname #1/basename #1 .tif.png}
\usepackage{multicol}

\usepackage[sorting=nyt, citestyle=authoryear, bibstyle=authoryear, isbn=false, firstinits=true, url=false, terseinits=true, dashed=false, maxcitenames=3, maxbibnames=99, backref=true, doi=false]{biblatex}

\title{Brief Article}
\author{The Author}
%\date{}                                           % Activate to display a given date or no date

\begin{document}
\maketitle
%\section{}
%\subsection{}

\begin{multicols*}{2}
\parencite{Soderberg2010}
\end{multicols*}{2}

\printbibliography

\end{document}


This doesn't work:

\documentclass[11pt]{amsart}
\usepackage{geometry}                % See geometry.pdf to learn the layout options. There are lots.
\geometry{letterpaper}                   % ... or a4paper or a5paper or ...
%\geometry{landscape}                % Activate for for rotated page geometry
%\usepackage[parfill]{parskip}    % Activate to begin paragraphs with an empty line rather than an indent
\usepackage{graphicx}
\usepackage{amssymb}
\usepackage{epstopdf}
\DeclareGraphicsRule{.tif}{png}{.png}{convert #1 dirname #1/basename #1 .tif.png}
\usepackage{multicol}

\usepackage[sorting=nyt, citestyle=authoryear, bibstyle=authoryear, isbn=false, firstinits=true, url=false, terseinits=true, dashed=false, maxcitenames=3, maxbibnames=99, backref=true, doi=false]{biblatex}

\title{Brief Article}
\author{The Author}
%\date{}                                           % Activate to display a given date or no date

\begin{document}
\maketitle
%\section{}
%\subsection{}

\begin{multicols*}{2}
\parencite{Soderberg2010}
\end{multicols*}{2}

\begin{multicols*}{2}
\printbibliography
\end{multicols*}{2}

\end{document}


The only difference is that the second document has the reference list inside multicols.

-
Please add to your question a minimal working example illustrating the problem. –  Gonzalo Medina May 16 '13 at 2:01
Minimal working example added. –  daviewales May 16 '13 at 3:44
The extra letter spacing is due to the fact that the bibliography text is justified. You can see this if you switch to ragged right text with \appto{\bibsetup}{\raggedright} in your preamble. –  Audrey May 16 '13 at 17:39

biblatex gives some small stretchability in URL breaking using url package \Urlmuskip parameter. This is there whether or not multicolumn is used, it's just that in the narrow measure of a multi column setting the stretchability is more likely to be used if available.

There is probably a higher level biblatex setting for this, but this just patches the setup command to reset the parameter to zero.

\toks0\expandafter{\biburlsetup}
\edef\biburlsetup{\the\toks0 \Urlmuskip =0mu\relax}


produces

-
Thanks for that! =D –  daviewales May 17 '13 at 0:54

I discovered that the problem was due to multicolumn. My solution was to disable multicolum for the reference list. If anyone has a solution that doesn't require disabling multicolumn for the reference list I will be very interested.

-
Kindly add the MWE as requested by Gonzalo Medina. It will add value to the Question and Answer while benefiting others to post new answers and future users. I are not aware of how multicolumn was a problem and how disabling resolved it because of absence of sample code ?. MWE is first step to diagnosis of errors/issues –  texenthusiast May 16 '13 at 2:06
Minimal working example added. –  daviewales May 16 '13 at 3:45