[File-writer API] Details on NotReadableError and the snapshot state

Hi,

For context, I'm currently working on a Tizen (based on a somewhat modern
Webkit) web app and trying to store a file (on an actual Tizen test
device). As far as documentation, Tizen linked to specs, so here I am :-)
I managed to get a FileSystem instance, but fail to get a FileEntry (code:
4) after fs.getFile(validString, {create: true}) (file isn't supposed to
exist, but that should irrelevant according to the spec)

First, what is error 4 for fs.getFile? Remote devtools suggests that error
codes are the same for fs.getFile than any other File error, but this isn't
very clear from the file-writer spec.
Second, the .getFile function lists a bunch of error cases, but nowhere is
written which error and code should be provided. The wording is always
"getFile *MUST* fail" which doesn't seem really helpful either for other
implementors to implement nor for authors to understand whats' going on.
Did I miss something on this section?

code:4 aka NotReadableError in FileError can happen "due to permission
problems that occur after a snapshot state has been established". I guess
I'm looking at a Webkit bug? (I bet more on a device bug...) The spec
doesn't help to say.

Any help in understanding how code:4 can happen on fs.getFile would be
appreciated especially.

Thanks,

David