Fonts rendering differences

[ilu]

Since I've paid some attention to font rendering lately I noticed that some fonts render very differently in different applications. I'm posting some screens from Double Commander (left) and Krusader (right), always the regular/book version 11pt. I know that Krusader has QT and DC is compiled with GTK+ but because of that DC should render correctly and Krusader not. Instead it's the other way round. Fonts in DC are almost bold. Only Clear Sans (first screen) looks almost the same. Does anybody know why?