manual/include/kde-plasma-5.html

<p>
  Under <dfn>KDE Plasma 5</dfn>, plugin and various other windows will not stay
  on top of any main window; therefore a workaround is required.
</p>

<h2>Workaround for ancillary windows not staying on top in KDE Plasma 5</h2>

<p>
  In order to force ancillary windows in Ardour to stay on top, the following
  steps are necessary:
</p>

<ol>
  <li>Launch the <kbd class="menu">System Settings</kbd> application.</li>
  <li>Open <kbd class="menu">Workspace &gt; Window Managment</kbd>.</li>
  <li>Select <kbd class="menu">Window Rules</kbd> in the left-hand sidebar. It
  should default to the <kbd class="menu">Window matching</kbd> tab.</li>
  <li>Click on the <kbd class="menu">New...</kbd> button.</li>
  <li>On the line that says <kbd class="menu">Window class (application)</kbd>,
  set the combo box to <kbd class="menu">Substring Match</kbd> and type <kbd
  class="user">ardour</kbd> in the text entry field.</li>
  <li>In the list box that is labeled <kbd class="menu">Window types:</kbd>,
  click on the option <kbd class="menu">Dialog Window</kbd>, then press and
  hold <kbd>Ctrl</kbd> while clicking on the second option <kbd
  class="menu">Utility Window</kbd>.</li>
  <li>Select the <kbd class="menu">Arrangement & Access</kbd> tab.</li>
  <li>Check the box next to the <kbd class="menu">Keep above</kbd> option. On
  the same line, select <kbd class="menu">Force</kbd> from the combo box, then
  click on the <kbd class="menu">Yes</kbd> radio button for that line.</li>
  <li>Click on the <kbd class="menu">OK</kbd> button to dismiss the dialog.
  </li>
</ol>

<p>
  At this point you can close the <kbd class="menu">System Settings</kbd>
  application.
</p>

<h3>Background Info</h3>

<p>
  <a href="https://bugs.kde.org/show_bug.cgi?id=172615#c26">According to one of
  the lead KDE developers</a>, they are not willing to follow the <abbr
  title="Inter-Client Communication Conventions Manual">ICCCM</abbr> standard
  for utility windows. Apparently they are alone in this understanding, as
  plugin windows on Ardour under Linux work out of the box on every other <abbr
  title="Window Manager">WM</abbr> out there.
</p>

<p>
  Under KDE 4, there was a workaround in Ardour (<kbd class="menu">Preferences
  &gt; Theme &gt; All floating windows are dialogs</kbd>) that would "trick"
  KDE into forcing certain window types to be on top of their parent windows,
  but this no longer works under KDE Plasma 5.
</p>