Remove input-prepend and input-append for singular .input-group. The classes
have changed for the elements within,and require a bit more markup to use
buttons:

• Use .input-group as the parent class around the input and addon.
• For text based prepends/appends,use .input-group-addon instead of .addon.
• For button prepends/appends,
  use .input-group-btn and place your .btn within that element.

例：

<div class="container">
  <div class="row">
    <div class="col-sm-3 col-xs-12 col-lg-3">
      <form class="form-search">
          <div class="input-group">
              <input type="text" class="form-control " placeholder="Text input">
              <span class="input-group-btn">
                  <button type="submit" class="btn btn-search">Search</button>
              </span>
          </div>
      </form>
    </div>
  </div>
</div>

编辑：从@kviktor和@ max4ever的工作示例：

http://bootply.com/75917

http://bootply.com/78014