Document "readonly" state not reset after reload

I load a document with only or without, then I realize I'll need to persist it, so I reload it. The missing attributes are loaded now, but the document still appears as read-only and cannot be saved.

Example:

f = Fund.without(:prices).find('5167f7dc0ea8c8affc0005b2')

p f.readonly?, f.__selected_fields, f.prices.count

f.reload

p f.readonly?, f.__selected_fields, f.prices.count

Output:

true

{"prices"=>0}

0

true

{"prices"=>0}

1010