Some fonts not listed in font dialog

I am using SoulseekQT 2013.11.6 on Linux 3.12.7 with Qt4 4.8.5.

I have noticed, when customizing the SoulseekQT font, not all fonts installed on my system are listed in the dialog which appears. For example. I want to use the 'Tahoma' TrueType font which I have installed, but SoulseekQT doesn't list it. Can anyone explain suggest the reason for this and better still, a workaround?