How to prevent CKEditor replacing spaces with  ?

Based on Reinmars accepted answer and the Entities plugin I created a small plugin with an HTML filter which removes redundant   entities. The regular expression could be improved to suit other situations, so please edit this answer.

/*
 * Remove   entities which were inserted ie. when removing a space and
 * immediately inputting a space.
 *
 * NB: We could also set config.basicEntities to false, but this is stongly
 * adviced against since this also does not turn ie. < into &lt;.
 * @link http://stackoverflow.com/a/16468264/328272
 *
 * Based on StackOverflow answer.
 * @link http://stackoverflow.com/a/14549010/328272
 */
CKEDITOR.plugins.add('removeRedundantNBSP', {
  afterInit: function(editor) {
    var config = editor.config,
      dataProcessor = editor.dataProcessor,
      htmlFilter = dataProcessor && dataProcessor.htmlFilter;

    if (htmlFilter) {
      htmlFilter.addRules({
        text: function(text) {
          return text.replace(/(\w)&nbsp;/g, '$1 ');
        }
      }, {
        applyToAll: true,
        excludeNestedEditable: true
      });
    }
  }
});

These entities:

// Base HTML entities.
var htmlbase = 'nbsp,gt,lt,amp';

Are an exception. To get rid of them you can set basicEntities: false. But as docs mention this is an insecure setting. So if you only want to remove  , then I should just use regexp on output data (e.g. by adding listener for #getData) or, if you want to be more precise, add your own rule to htmlFilter just like entities plugin does here.