ES 1.2.0 MapperParsingException when create default mapping with 'include_in_all' nested

One noticeable issue found with ES 1.2 during our deployment is that it threw exception when created default mappings with ‘include_in_all’ nested under it (doesn’t matter it’s set to true/false). For example, the following index creation command returns error when against ES 1.2 but it works well against ES 1.1.

PUT test
{
"mappings": {
"default": {
"include_in_all": true
}
}
}

Result
{
"error": "MapperParsingException[mapping [default]]; nested: MapperParsingException[Root type mapping not empty after parsing! Remaining fields: [include_in_all : true]]; ",
"status": 400
}

Is this a regression with ES 1.2?