Redmine

I can confirm this - I'm seeing the same thing. It's the custom_fields that cause this.

Something strange:
to create an issue with a custom field we do

1issue = Issue.new(
2  :subject => 'REST API',
3  :assigned_to_id => 1,
4  :project_id => 1,
5  :custom_field_values => {'2' => 'Fixed'}
6)
7issue.save

but when I retrieve an issue with REST API, :custom_field_values is not an entry of the attributes hash. Instead, I have a :custom_fields entry containing a custom_field entry which is an array containing all custom fields values.
If a try to update one of those values like that

1issue = Issue.find(1)
2issue.custom_fields.custom_field[0] = dummy_value
3issue.save

C:/Ruby187/lib/ruby/gems/1.8/gems/activesupport-2.3.5/lib/active_support/core_ext/array/conversions.rb:163:in `to_xml': Not all elements respond to to_xml (RuntimeError)

So, I can't find a way to update a custom field.

In fact, it's possible to update a custom fields with the same hash than for creation, but you must also nilify custom_fields

1issue = Issue.find(1)
2issue.custom_field_values = {'1' => 'dummy'}
3issue.custom_fields = nil
4issue.save

Stéphane Dubois wrote:

In fact, it's possible to update a custom fields with the same hash than for creation, but you must also nilify custom_fields
[...]

I don't know which version you're using but I can't reproduce this problem with current trunk. The following works:

1issue = Issue.find(1)
2issue.custom_field_values = {'1' => 'dummy'}
3issue.save