In Custom workflow 2011 Update on Entity, updates all the fields even though nothing changed.

Hello,

I have a custom workflow step which retrieves an entity record, and updates some fields by running IOrganizationService.Update(Entity), but when I see the audit history for that entity, all the fields (including non changed fields values) get updated. May be they are getting overridden. Do I have to check anything in my C# code to handle this?

Thanks,

Alok N