Regression: Qt5 doesn't handle Arial on Windows 7 well

Set the QPlainTextEdit font to Arial, and Thai characters are rendered much smaller than English characters. The attached screen shots are from running the attached application under Qt 4.8.6 and Qt 5.3.1, both compiled from source, on the same Windows 7 pro x64.

The same issue occurs when we paint text on a QGraphicsItem using a QPainterPath: it's fine under Qt 4.8.6, but Thai is very small under Qt 5.3.1.

FWIW, the default font "MS Shell Dlg 2" displays the English and Thai the same size under Qt 5.3.1 for both QPlainTextEdit and QGraphicsItem, so it seems the problem is specific to certain kinds of fonts.

Qt 4.8.6 was configured with:

configure -plugin-sql-sqlite -no-qt3support -developer-build -opensource -qtlibinfix _fmosoft -platform win32-msvc2008

Qt 5.3.1 was configured with:

configure -prefix %CD%\qtbase -developer-build -opensource -no-c++11 -nomake tests -no-compile-examples -no-opengl -no-angle -plugin-sql-sqlite -platform win32-msvc2008 -confirm-license -qtlibinfix _fmosoft -make-tool jom

Since we ported to Qt 5, this issue is preventing us from releasing our application.