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"Cannot be fixed" sounds pretty final, and also a little
pessimistic.  From your description, it seems that the
correct functionality could be maintained at the cost of
retention of the keys in "normal locals" and dissection back
into "fast locals" and "normal locals" after the trace
function does ... whatever it does.  In particular, it seems
unacceptable that the invariants of the semantics of class
creation (on which introspection and other important
functionality depends) is borked by debugging in such a way
as to render quite misleading the process of debugging code
that depends on those invariants.

Not to mention that the workaround ("be sure to rename your
class factory function parameters so that they don't collide
with intended attributes of the created class") just makes
Python seem ... lame.

I hope for a more optimistic reply.