Comment 2 for bug 557333

Correction: it was the validation

debugging before and after the line 221 on webapi.py:

       defaults.setdefault('_unicode', True)

the contents of the "defaults" dict varies (1 is before, 2 is after that line):

1 {'_unicode': False, 'myfile': {}} -> ['myfile'] 992166
2 {'_unicode': False, 'myfile': {}} -> ['myfile'] 992166
1 {} -> ['myfile'] 992166
2 {'_unicode': True} -> ['myfile'] 992166

This is the output for 1 upload POST request, running through validation and accessing it later. It seems the contents are emptied somehow, and then the default _unicode value is applied to the uploaded file, which causes the break.