When a string written in Thai is displayed on a label then it will not be rendered correctly

When a string written in Thai is displayed on a label then it will not be rendered correctly, however on a lineedit it will be displayed just fine. Attached is an example that can be used to reproduce this, the xml file contains strings which can be pasted into the lineedit (then press apply) to display on the label.

This works fine on Windows but not on Mac OS X.