Well per the documentation, QByteArray is implicitly null-terminated:
http://qt-project.org/doc/qt-4.8/qbytearray.html#details
but QByteArray::size does not include the null terminator.

Also, a non null-teriminated QByteArray can be created:
http://qt-project.org/doc/qt-4.8/qbytearray.html#fromRawData 
which shouldn't matter in this case, but well you can chalk this up to paranoia.