This was tested on a CentOS 7 server (apache 2.4.6, php 5.4.16) using a recent (post 3.5.0-beta) Joomla version from the master branch (specifically 11a1462). Really, though, the version shouldn't matter much.

To test:

With the web server's document root being '/var/www/html', create the necessary directories and install Joomla at '/var/www/html/foo/b a%20 \r2'. In other words:

# mkdir -p '/var/www/html/foo/b a%20 \r2'
# cd '/var/www/html/foo/b a%20 \r2'
# wget https://github.com/joomla/joomla-cms/archive/11a14629fce671670399ec7775caed4e7b5b92c1.zip
# unzip *.zip && rm *.zip -f
# 

Now attempt to access Joomla at http://example.com/foo/b%20a%2520%20%5Cr2/installation/index.php.

The page loads, but none of the related page resources are found or loaded.

Here's a look at some of the links to those resources in the HTML source for the page:

  <link href="/foo/b a%20 /r2/installation/favicon.ico" rel="shortcut icon" type="image/vnd.microsoft.icon" />
  <link rel="stylesheet" href="/foo/b a%20 \r2/media/jui/css/bootstrap.min.css" type="text/css" />
  <link rel="stylesheet" href="/foo/b a%20 \r2/media/jui/css/bootstrap-responsive.min.css" type="text/css" />
  <link rel="stylesheet" href="/foo/b a%20 \r2/media/jui/css/bootstrap-extended.css" type="text/css" />
  <link rel="stylesheet" href="/foo/b a%20 \r2/installation/template/css/template.css" type="text/css" />
  <link rel="stylesheet" href="/foo/b a%20 \r2/media/jui/css/chosen.css" type="text/css" />
  <script src="/foo/b a%20 \r2/media/jui/js/jquery.min.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/jui/js/jquery-noconflict.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/jui/js/jquery-migrate.min.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/system/js/html5fallback.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/jui/js/bootstrap.min.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/jui/js/chosen.jquery.min.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/system/js/mootools-core.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/system/js/core.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/system/js/mootools-more.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/system/js/punycode.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/media/system/js/validate.js" type="text/javascript"></script>
  <script src="/foo/b a%20 \r2/installation/template/js/installation.js" type="text/javascript"></script>

The problem is that Joomla's base path in those links has not been URL % encoded. They contain /foo/b a%20 \r2, whereas the should contain /foo/b%20a%2520%20%5Cr2.