Known Issue?
This really isn't the correct section.
Yes, it is a known issue. And it kind of is the correct section as it was just asking for why it happened, not reporting a bug. It, like Golrith said, is an issue with multiple mod registering fluid.steam
This has been around since the beginning of the 1.6.4 packs, and is even shown in DW20's Singleplayer series.
In-world steam looks normal, in GUI's though it is bugged. It only happens to steam when you have multiple steam mods installed (though I think Factorization is the main culprit.
(Looking back on that it seemed a bit rude in the way i wrote, I apologize as that was not my intention)