The quotes caused the encoded word to be taken literally which is the proper behavior. This could be defended against by checking if the name looks like an RFC 2047 encoded word and trying to decode it, but I don't think it's worth it so I'm marking this invalid.
It turns out this issue is a broken MUA composing the message. The encoded word in the header was quoted. The actual From: was like
From: "=?utf- 8?b?Sm9obiBEb2U =?=" <email address hidden>
The quotes caused the encoded word to be taken literally which is the proper behavior. This could be defended against by checking if the name looks like an RFC 2047 encoded word and trying to decode it, but I don't think it's worth it so I'm marking this invalid.