Doctrine\ODM\MongoDB\Mapping\ClassMetaData is loosing "file" property after serialization

After ClassMetaData is awakened it looses the "file" property and that breaks our File model.
File::count() returns 0

I dumped ClassMetaData object with caching enabled and disabled. Here's the diff:

146c146
< [file] =>
—
> [file] => file
149a150,180
> [0] => Array
> (
> [keys] => Array
> (
> [uploaded_at] => 1
> )
>
> [options] => Array
> (
> [safe] => true
> [unique] =>
> )
>
> )
>

The first line is the missing file value. The second block appears to be missing indexes but I'm guessing this information should not be serialized.