From what I recall of the syntax, this fragment from kpanelapplet.cpp
in kdelibs-3.5.13 *looks* like it's making direct calls into QT3's 
namespace (not tqtinterface's), even though it doesn't #include any
QT files, just TQT stuff:

Qt::Orientation KPanelApplet::orientation() const
{
  if( _position == pTop || _position == pBottom ) {
    return Qt::Horizontal;
  } else {
    return Qt::Vertical;
  }
}

My understanding is, the QT namespace is included in this code
via TQT, allowing the code to compile.

If so, this might explain the lengthy linking bug I posted a little
while ago (--as-needed does not like transitive dependencies like
this).  Can someone confirm that this is in fact what is happening?
I haven't written a line of C++ code in ~15 years, so I'm not sure
I remember how it works.

If I'm right, I'll go ahead and file the bug, but I don't want to
clutter Bugzilla with non-issues.