When the Salesforce API returns multiple errors, none of them are logged.

Here's an example of an API error response that is not logged (or even reported) by the salesforce module:

Requesting POST /services/data/v27.0/sobjects/CampaignMember HTTP/1.0
{"CampaignId":"xxxx0000000xxxxxxx","ContactId":null}

[{"message":"Attempted to add a campaign member where either the member id 'null' or the campaign id 'xxxx0000000xxxxxxx' is null.","errorCode":"REQUIRED_FIELD_MISSING","fields":[]},{"message":"Attempted to add a campaign member where either the member id 'null' or the campaign id 'xxxx0000000xxxxxxx' is null.","errorCode":"REQUIRED_FIELD_MISSING","fields":[]}]