admin broken on FileField with blank=True

[malte]

If you have a FileField declared like so:
image_1 = models.FileField(upload_to=get_image_path, null=True, blank=True)

Then in django admin, the field becomes voluntary as it should. If you save a file in an optional field that works as expected. But if you come back to the item in the admin, and just hit 'save' without touching the optional file that is uploaded, the db record gets updated with a blank value for the FileField, effectively killing the connection with the file.

I'm using Sqlite, may make a difference here I suppose.