Are images of the early Mickey Mouse still copyrighted?

The LA Times's Joseph Menn has a great, well-researched feature article on the history of the copyright for the image of Mickey Mouse as portrayed in the earliest Disney cartoons -- and the theory that Disney made mistakes early on with its copyright registration, placing images of that specific Mickey (not the Mickey we know today) in the public domain. Prominent legal scholars like Peter Jaszi agree, but who will shell out the millions in legal fees to prove it? After all, the company's already threatened legal action against law-students who publish papers investigating the question!

Brown went searching for flawed formalities -- and found one. It was on the title card at the beginning of a "Steamboat Willie" cartoon that had just been rereleased on a 1993 LaserDisc honoring Mickey's 65th birthday. It said in full:

"Disney Cartoons
Present
A Mickey Mouse
Sound Cartoon
Steamboat Willie
A Walt Disney Comic
By Ub Iwerks
Recorded by Cinephone Powers System
Copyright MCMXXIX."

[...]

The authoritative legal treatise "Nimmer on Copyright" says that a copyright is void if multiple names create uncertainty, and courts have agreed. In 1961, a federal judge in Massachusetts cited the "accompanied by" rule in throwing out a copyright claim by newspaper cartoonist Art Moger. Moger's name was included in the title above his panels, but the name of another artist ran inside the boxes.

Disney's rights to young Mickey Mouse may be wrong (Thanks, Xeni!)