The following code results in a segfault on the second evaluateTo line:

==
QXmlQuery xq;
QString out;
xq.setFocus("<test>valid-input</test>");
xq.setQuery("/test");
xq.evaluateTo(&out);
xq.setFocus("invalid-input");
xq.setQuery("/query2");
xq.evaluateTo(&out);
==

==
Thread 1 (Thread 0x7ffff7fbd760 (LWP 6664)):
#0 0x0000000000000000 in ?? ()
#1 0x00007ffff5cde89d in ?? () from /usr/lib/libQtXmlPatterns.so.4
#2 0x00007ffff5c87772 in ?? () from /usr/lib/libQtXmlPatterns.so.4
#3 0x00007ffff5d32bae in ?? () from /usr/lib/libQtXmlPatterns.so.4
#4 0x00007ffff5cabcc9 in ?? () from /usr/lib/libQtXmlPatterns.so.4
#5 0x00007ffff5ca0681 in ?? () from /usr/lib/libQtXmlPatterns.so.4
#6 0x00007ffff5c87889 in ?? () from /usr/lib/libQtXmlPatterns.so.4
#7 0x00007ffff5c36549 in QXmlQuery::evaluateTo(QAbstractXmlReceiver*) const () from /usr/lib/libQtXmlPatterns.so.4
#8 0x00007ffff5c36670 in QXmlQuery::evaluateTo(QString*) const () from /usr/lib/libQtXmlPatterns.so.4
==