once format on resource form has errored, no longer submits form

[shevski]

Steps to reproduce:

1. go to edit a resource, e.g. ​http://s031.okserver.org:2375/dataset/ted/resource_edit/a621a6ad-6f1c-46d1-b858-03cdb7a25c07
2. Change the format field to something it doesn't get. e.g. add a comma "HTML,"
3. Get message: "The form contains invalid entries:

Last modified: Date format incorrect Size: Invalid integer"

4. Format field reverts, try to re-save/submit form - i.e. click on "update resource"
5. nothing happens (same if you even try changing the format field