This issue is fixed for the next build.
Looks like a fix was made to v24 that exposed this bug.
Easy to explain the issue. When QFontMetrics (a Qt class) is used, you need to specify the device. If you don't specify the device, you can't rely on the any font calculations because they may be calculated against the wrong device. For example, when printing, you must specify the printer device or you will always get the wrong calculation. In this case, a QWidget must be specified for the device.
What makes this bug so sneaky is that when you don't specify a device, on some platforms it will work all the time. On other platforms, it will work with some displays and not others.