title: Solr sorting with group.sort and sort returns inappropriate order
body: <p>We use solr for our product search. As products we have variants of base products (e.g. a shirt could have variants for the colors red, green, yellow etc.) and each variant is a document in our solr index.</p>
  
  <p>Now we have a requirement to only show one product variant based on a rule set. (1. products in cart, 2. products on sale, 3. lowest price)
  I tried to solve this by grouping by a field common to all variants per product (called base_string in this example) and sort the group based on the rule set.
  This works fine but when I sort by the price (price_double field) in descending orderi get a unexpected result.</p>
  
  <p>For example if I have this documents:</p>
  
  <pre><code>{
      "id": "000101",
      "name_string": "Test 1.1",
      "base_string": "0001",
      "price_double": 11.5,
      "test_boolean": true
  },
  {
      "id": "000102",
      "name_string": "Test 1.2",
      "base_string": "0001",
      "price_double": 10.5,
      "test_boolean": true
  },
  {
      "id": "000103",
      "name_string": "Test 1.3",
      "base_string": "0001",
      "price_double": 1.5,
      "test_boolean": true
  },
  {
      "id": "0002",
      "name_string": "Test 2",
      "base_string": "0002",
      "price_double": 5.5,
      "test_boolean": true
  },
  {
      "id": "0003",
      "name_string": "Test 3",
      "base_string": "0003",
      "price_double": 55.5,
      "test_boolean": true
  }
  </code></pre>
  
  <p>I query the 3 relevant products with following query sorted by price_double in ascending order:</p>
  
  <pre><code>q=test_boolean%3Atrue&amp;sort=price_double+asc&amp;wt=json&amp;indent=true&amp;group=true&amp;group.field=base_string&amp;group.sort=price_double asc
  </code></pre>
  
  <p>The result seems fine (000103 (Price: 1.5), 0002 (Price: 5.5), 0003 (Price 55.5)).</p>
  
  <p>If I sort by price_double in descending order I get a result with a, for me, unlogical order:</p>
  
  <pre><code>q=test_boolean%3Atrue&amp;sort=price_double+asc&amp;wt=json&amp;indent=true&amp;group=true&amp;group.field=base_string&amp;group.sort=price_double desc
  </code></pre>
  
  <p>The result is: 0003 (Price 55.5), 000101 (Price 1.5), 0002 (Price 5.5)</p>
  
  <p>Why do I get a wrong order if I sort by price_double in descending order?
  Does the group sort happens after the document sort?</p>
  
  <p>Any ideas how I could solve this?</p>