Comment 4 for bug 98380

...Of course, this bug was first reported in 2004, and apparently hasn't bothered anyone else since then.

And ClassType is, itself, an ahem "newstyle class".

But truly, registering adapters against the class "ClassType" itself is exceedingly rare; if this is some terrible implementation detail preventing it from working without unreasonable tricks, it wouldn't bother me to see it just be a documented limitation.