bug: In browsable API HTML forms boolean fields do not change correctly

Hi, I am using REST framework v3.1.1 and I noticed that BooleanFields on the HTML form inside the
browsable API does not take effect and change the data as expected.

To reproduce:
Make a serializer with some boolean fields
In the browsable API's HTML form, try to edit the boolean checkbox
Compare the result returned with the expected output

Every time I have to explicitly change the values in the raw data for the expected change to occur
before the POST and PUT request is made

I have also just noticed that you can change them from false to true then it will change as expected, but once they are set to true you cannot change it to false using the HTML form.

[maryokhin]

I noticed the same behaviour before, but dismissed on lack of coffee.

[tomchristie]

This was occuring if required=False was also set in the field - so will have tended to be seen by users of automatic ModelSerializers, rather than users of Serializer. Now resolved.