I have a record schema with fields that look like this:
"fields" : [
  {
    "name" : "a",
    "type" [ "null", "string" ],
    "default" : null
  },
  {
    "name" : "b",
    "type" [ "null", "string" ],
    "default" : null,
    "aliases" : ["a"]
  }
]

Basically b is a copy of a where we hoped avro would do the copying for us.
In the output b does get populated properly, but a does not: it contains
all nulls.
Now i can see how this is abuse of avro: i should be doing the copy myself
outside of avro. However the fact that this did not bomb and produced
incorrect results (a all nulls) worries me a bit. This can lead to subtle
bugs in my opinion.

I am using an old version (1.5.4) so perhaps this is an outdated
observation.