I did a completely clean pull from upstream and only changed the fontstring, so no other config changes at all were present in my build.
The font string I was using is: "DejaVu Sans Mono:size=10" (and I just tested with "DejaVu Sans Mono:size=9" just in case that was a point of difference while composing this and everything continued to function fine) I'm unsure what the problem could be, but have you tried a different font? Maybe it's something with either your version of DejaVu Sans Mono?
