Qt4 segfault on mlab.mesh()

I have installed `mayavi 4.4.4`, based on `Python 2.7.12`, `VTK 6.3.0` and `Qt 4.8.7`. My system is Arch Linux. I can `import mayavi` and minimal examples of `traitsui` open `Qt` windows as expected. But when I try to run the first `mlab` [demo](http://docs.enthought.com/mayavi/mayavi/mlab.html#a-demo), I am presented with a segfault on the line:

``` python
s = mlab.mesh(x, y, z)
```

The stack as reported by `gdb` is:

```
Program received signal SIGSEGV, Segmentation fault.
#0 0x00007fffee559804 in QObject::moveToThread(QThread*) () from /usr/lib/libQtCore.so.4
#1 0x00007fffee522d7e in QFactoryLoader::instance(QString const&) const () from /usr/lib/libQtCore.so.4
#2 0x00007fffec1abf35 in ?? () from /usr/lib/libQtGui.so.4
#3 0x00007fffec1acf55 in ?? () from /usr/lib/libQtGui.so.4
#4 0x00007fffec1ae7e8 in QImageReader::read(QImage*) () from /usr/lib/libQtGui.so.4
#5 0x00007fffec1ae9d4 in QImageReader::read() () from /usr/lib/libQtGui.so.4
#6 0x00007fffec1c221a in QPixmapData::fromFile(QString const&, char const*, QFlags) () from /usr/lib/libQtGui.so.4
#7 0x00007fffec1bac34 in QPixmap::load(QString const&, char const*, QFlags) () from /usr/lib/libQtGui.so.4
#8 0x00007fffec1bc9e0 in QPixmap::QPixmap(QString const&, char const*, QFlags) () from /usr/lib/libQtGui.so.4
#9 0x00007fffed1d1c45 in ?? () from /usr/lib/python2.7/site-packages/PyQt4/QtGui.so
#10 0x00007fffed1d1faa in ?? () from /usr/lib/python2.7/site-packages/PyQt4/QtGui.so
#11 0x00007fffeeda7643 in ?? () from /usr/lib/python2.7/site-packages/sip.so
#12 0x00007ffff7a95ced in type_call () from /usr/lib/libpython2.7.so.1.0
#13 0x00007ffff7a3c662 in PyObject_Call () from /usr/lib/libpython2.7.so.1.0
#14 0x00007ffff7ad9665 in PyEval_EvalFrameEx () from /usr/lib/libpython2.7.so.1.0
...
```