Version:            (using Devel)
Installed from:    Compiled sources
Compiler:          gcc (GCC) 4.2.3 (Ubuntu 4.2.3-2ubuntu7)  
OS:                Linux

I use KDE4 from SVN and am seeing this problem for some time, but did not want to report it before, as I was not sure that something was not wrong with my configuration (~/.kde4). Recently I have reinstalled my system with Ubuntu Hardy and have yesterday build KDE4 from SVN (almost beta1 state), removed my configuration (rm -rf ~/.kde4) and started KDE4.

I change all font sizes to be 1pt less than it is default in KDE4. This is my config from kdeglobals:
[General]
XftAntialias=true
XftHintStyle=hintfull
XftSubPixel=rgb
desktopFont=Sans Serif,9,-1,5,50,0,0,0,0,0
fixed=Monospace,9,-1,5,50,0,0,0,0,0
font=Sans Serif,9,-1,5,50,0,0,0,0,0
menuFont=Sans Serif,9,-1,5,50,0,0,0,0,0
smallestReadableFont=Sans Serif,7,-1,5,50,0,0,0,0,0
taskbarFont=Sans Serif,9,-1,5,50,0,0,0,0,0
toolBarFont=Sans Serif,7,-1,5,50,0,0,0,0,0

Sometimes, when I logout/reboot and login again, some of the fonts sizes are reset back to normal size (1pt larger). This is the diff of kdeglobals after this happens:
 [General]
-XftAntialias=true
-XftHintStyle=hintfull
 XftSubPixel=rgb
 desktopFont=Sans Serif,9,-1,5,50,0,0,0,0,0
-fixed=Monospace,9,-1,5,50,0,0,0,0,0
-font=Sans Serif,9,-1,5,50,0,0,0,0,0
-menuFont=Sans Serif,9,-1,5,50,0,0,0,0,0
 smallestReadableFont=Sans Serif,7,-1,5,50,0,0,0,0,0
-taskbarFont=Sans Serif,9,-1,5,50,0,0,0,0,0
 toolBarFont=Sans Serif,7,-1,5,50,0,0,0,0,0

I think it is always the same fonts that are lost, but I am not 100 sure. Will keep an eye on this in future and report back.