migrate produces wrong default value, causes saving new nodes to fail

I tried creating a brand new blank test site and there I do not have the problem. The original site with the problem was migrated from D6, so my new guess is the problem was introduced in the migration.

Looking at the field_config_instance DB tables, there seems a difference between the way default_value for the two fields is stored. (I set no default value for either one.) I don't know enough about the tables to really figure it out, but the new field has like this:
... \"default_value\";N; ...

but the old one doesn't has the N. It looks like:
... \"default_value\";a:1:{i:0;a:1:{s:5:\"value\";s:0:\"\";}} ...

Is this significant? What does the N mean?

Did some digging around the drupal website and found out the function to print the field config instance values. Using it from devel, like so:

print_r (field_read_instances());

I find out that the migrated integer field have array for default_value, like this:

[default_value] => Array
                (
                    [0] => Array
                        (
                            [value] => 
                        )

                )

but newly created field have a single value, like this:

            [default_value] => 
            [id] => 9

Seem like this might be the problem?

I am willing to test a fix if you can tell me what to try.

OK, I did more digging and found out how to hack the data field in the SQL. If I change it into a single value (N) like the new field's, then the problem for saving new nodes without an entry in each integer field is resolved.

This shows that the problem with the migrated integer / number fields is that the default_value is made an array when it needs to be a single value.

Have changed priority to major as this will be a major problem when people try to add new nodes to migrated sites. I didn't see any issues in the queue that address this.