Metadata edit: modifications are not saved after a validation error

Steps to reproduce:

1. Edit the metadata of a document with Drive.
2. Fill in the description and / or other metadata.
3. Put some text in the Expiration date field.
4. Click Save.
   -> You get a validation error. Already filled in values are kept.
5. Select a date in the Expiration date field.
6. Click Save.
   => Feedback message says that document has been modified but changes are not saved.