Hi,
The thousands separators in all mods are bugged, it shows as an NBSP symbol from the Minecraft font and it looks like this: http://i.imgur.com/Dv7x7v9.png
I reckon it has something to do with the system localization settings because for me it persisted between multiple hardware reconfigurations and OS reinstallations, and I've never seen something like this on other peoples videos. From what I've tested, number settings don't seem to affect this, I tried to change my thousands separator in system settings and in-game I still saw that NBSP symbol.
I've found this topic: http://www.minecraftforge.net/forum/index.php?topic=3263.msg21515#msg21515
And I've also found this exact issue on Minecraft own bug tracker, but basically their response has been along the lines of "We have no use for a thousands separator in vanilla Minecraft, so you and your modding buddies can go fuck yourself".
Now I know this is not really an FML issue, but since FML is used in 99% of modded Minecraft installations, fixing this in FML would mean fixing it for the majority of people who are affected by this vanilla Minecraft bug.
