When updating a lead source, if it recognizes that there are campaign activities using that source, it will make the 'Source Activity' field visible and allow you to set this. This doesn't happen on lead creation, it will just show the source and then when the record is created the activity field is available but empty.
We should change this to be consistent, so when setting a source at creation it will check for campaign activities, and then make the source activity visible if there are campaign activities with that source.
