Removing some tests from tst_datepicker.qml can get rid of the segfault. But it seems like random which tests need to be removed. Even removing a single totally unrelated line of code can cause the segfault to appear/disappear.

So, with this tst_datepicker.qml http://paste.ubuntu.com/15684437/ I get these results:

tim@tim-mbp:~/dev/ubuntu-ui-toolkit/m/datepicker-segfault/tests/unit_x11/tst_components$ ../../unit/runtest.sh tst_components tst_datepicker.qml 
Executing dbus-test-runner --task gdb -p --quiet -n tst_datepicker.qml -m 300 -p --batch -p -ex -p 'set print thread-events off' -p -ex -p run -p -ex -p bt -p --return-child-result -p --args -p /home/tim/dev/ubuntu-ui-toolkit/m/datepicker-segfault/tests/unit_x11/tst_components/tst_components -p -input -p tst_datepicker.qml -p -maxwarnings -p 100 -p -o -p /home/tim/dev/ubuntu-ui-toolkit/m/datepicker-segfault/tests/test_tst_datepicker.qml.xml,xunitxml -p -o -p -,txt
Working directory: /home/tim/dev/ubuntu-ui-toolkit/m/datepicker-segfault/tests/unit_x11/tst_components
DBus daemon: unix:abstract=/tmp/dbus-yBhHzh27Dd,guid=4b8c2f760af281cfdce396a7570780bd
tst_datepicker.qml: Started with PID: 28887
Undefined command: "".  Try "help".
tst_datepicker.qml: [Thread debugging using libthread_db enabled]
tst_datepicker.qml: Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
tst_datepicker.qml: [New Thread 0x7fffeb5f7700 (LWP 28893)]
tst_datepicker.qml: [New Thread 0x7fffe136d700 (LWP 28894)]
tst_datepicker.qml: [New Thread 0x7fffe0b6c700 (LWP 28895)]
tst_datepicker.qml: [New Thread 0x7fffdbfff700 (LWP 28896)]
tst_datepicker.qml: [New Thread 0x7fffda792700 (LWP 28898)]
tst_datepicker.qml: ********* Start testing of components *********
tst_datepicker.qml: Config: Using QtTest library 5.5.1, Qt 5.5.1 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 5.3.1 20160225)
tst_datepicker.qml: PASS   : components::DatePickerAPI::initTestCase()
tst_datepicker.qml: QWARN  : components::DatePickerAPI::test_0_mode() file:///home/tim/dev/ubuntu-ui-toolkit/m/datepicker-segfault/tests/unit_x11/tst_components/tst_datepicker.qml:30:9: QML DatePicker: Theme.createStyleComponent() is deprecated. Use ThemeSettings instead.
tst_datepicker.qml: 
tst_datepicker.qml: Thread 1 "tst_components" received signal SIGSEGV, Segmentation fault.
tst_datepicker.qml: 0x00007ffff7b7c814 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #0  0x00007ffff7b7c814 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #1  0x00007ffff7b5ca49 in QV4::MemoryManager::mark() () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #2  0x00007ffff7b5d46b in QV4::MemoryManager::runGC() () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #3  0x00007ffff7b5e5f8 in QV4::MemoryManager::allocData(unsigned long, unsigned long) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #4  0x00007ffff7b4452a in QV4::ExecutionEngine::newString(QString const&) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #5  0x00007ffff7b7d8d4 in QV4::Heap::FunctionObject::FunctionObject(QV4::ExecutionContext*, QString const&, bool) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #6  0x00007ffff7b7f3a8 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #7  0x00007ffff7b7f7b9 in ?? () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #8  0x00007ffff7b7d20b in QV4::BuiltinFunction::call(QV4::Managed*, QV4::CallData*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #9  0x00007ffff7be00b3 in QV4::Runtime::callProperty(QV4::ExecutionEngine*, int, QV4::CallData*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #10 0x00007fffd94cb83d in ?? ()
tst_datepicker.qml: #11 0x00007fffffff18a0 in ?? ()
tst_datepicker.qml: #12 0x00007ffff7c73ab8 in QV4::QmlContextWrapper::registerQmlDependencies(QV4::ExecutionEngine*, QV4::CompiledData::Function const*) () from /usr/lib/x86_64-linux-gnu/libQt5Qml.so.5
tst_datepicker.qml: #13 0x00007fff00000001 in ?? ()
tst_datepicker.qml: #14 0x00007fffffff1870 in ?? ()
tst_datepicker.qml: #15 0x0000000000000000 in ?? ()
tst_datepicker.qml: Exited with status 65280
tst_datepicker.qml: Shutting down
DBus daemon: Shutdown
Error: 1 errors in tst_datepicker.qml (0 warnings)
Found 1 failures including warnings.