Font hinting problems in Dropbox, other Qt applications

I'm using Ubuntu 14.04 and font hinting works perfectly as usual, except for a couple of applications: Dropbox's preferences and Dwarf Therapist. Since they are both Qt apps, I figure that's where the issue is.

Here's a picture of Dropbox's preferences:

If you zoom in you'll see that the font hinting is in greyscale:

I created a ~/.config/fontconfig/fonts.conf file with this in it:

<match target="font">
   <edit name="rgba" mode="assign">
     <const>rgb</const>
   </edit>
</match>

That seems to get some color subpixel hinting, but then the letters look even thinner and wispier (here set in comparison with Diodon's preferences, which displays the system font properly):

Is there a way to get these fonts to display correctly? Ideally the application would obey Ubuntu's defaults (hinting, the font itself, etc.).

I did install qt4-qtconfig, as explained here, but that did nothing. I'm not sure if this is a bug (under what package would I file one?), or something weird with my install. I feel they should just work without without editing a font.conf file (since every other program in Ubuntu ignores those), though if someone can give me the right settings for the font.conf file I'll be happy.