Apparently in the new Feed the Beast Unhinged mod pack buckets require steel plates and a hammer. Which mod implements this change? This sounds like the kind of thing GregTech would do but I have been unable to confirm if that mod is in fact the culprit.
GregTech did in fact do it. It's hard to find documentation where this is stated officially but I've been roaming the FTB Forums and have confirmed that GregTech changed a lot of stuff after 1.4.7.