Writing the same data twice into a XML file results in two different XML files (attribute ordering differs)

When using QDomDocument to save our project data as XML, saving the very same project two times results in two different XML files. The two files differ in the ordering of their attributes. This is problematic as these files cannot be diffed, merged, etc. anymore. I didn't observe this behaviour in Qt 4.8. This bug report is not about the arbitrary ordering of XML attributes, but that the ordering of attributes changes eventhough no new attributes were added.