Kerning incorrect in some applications

In some Qt 5 applications (e.g. Plasma and KSnapshot), the font kerning is incorrect. The third screenshot shows the same words (in the same font) rendered as expected. As you can see, the spacing between letters is consistent, while in screenshots 1 and 2, it is not. For example, note the placement of the t in 'History' in screenshot 1 compared to screenshot 3.