Note: Below is the original page from the Bootlint documentation, some of the info here might not apply to Bootlint-NG!

.form-inline and .form-horizontal are meant as containers for form content and are typically used on <form>s (although using them on <div>s is also valid). .form-group is meant to contain a single label-field pair. Using .form-inline or .form-horizontal on .form-group doesn't make sense. Instead, put the .form-group within the .form-inline or .form-horizontal.

Wrong:

<div class="form-group form-inline">
  ...
</div>

<div class="form-group form-horizontal">
  ...
</div>

Right:

<div class="form-inline">
  <div class="form-group">
    ...
  </div>
</div>

<div class="form-horizontal">
  <div class="form-group">
    ...
  </div>
</div>