Given a default hello world Qt Quick application, created with the wizard.
We have a QTimer in a test class (see attached project) set to 1000ms interval.
The timer is set to singleshot.
We also have an QElapsedTimer.
We start both timers from main.cpp (testclass.start()).
The timeout signal of the QTimer is connected to a slot in the test class which prints a message with the elapsed() time from the QElapsedTimer and restarts the QTimer.
After some time (eg. 20 to 120 seconds) we observe a delay of about 5-12 seconds measured by the QElapsedTimer. The whole event loop seems to be lagging.

We could reproduce this behaviour on both Mavericks and Yosemite with Qt downloaded as binary package for mac os (64bit) from qt.io. We used 5.3.1, 5.3.2, and 5.4.1 all downloaded from qt.io as 64bit binary packages.

The issue is NOT reproducible on Windows 7 (Qt 5.2.1-msvc2010) and Linux (64bit) with Qt 5.3.1 (64bit gcc)

The issue is NOT reproducible on OS X when building as a console application using QCoreApplication (and not QApplication).