Active Record Association: why does @owner.@target.count yield a result of 1 when @owner.@target returns an empty array?

I have models in my Rails app:

Sales_Opportunity which has_many Swots.

I'm setting them up using FactoryGirl and running a test to show that when I delete my Sales_Opportunity I also cause the associated Swots to be deleted. For some reason when debugging with Byebug I'm getting strange results - the Sales_Opportunity and Swot records are being correctly created, but when I run sales_opportunity.swots it returns [ ] whereas sales_opportunity.swots.count returns 1. What's more odd is the exact same code works fine with anther object association (timeline_events are exactly like swots yet work perfectly with the same code).

Can anyone tell me what am I doing wrong please?

Sales_Opportunity.rb:

class SalesOpportunity < ActiveRecord::Base
 default_scope { order('close_date ASC') }
 belongs_to :user
 belongs_to :company
 has_many :key_contacts
 has_many :timeline_events, dependent: :destroy
 has_many :swots, dependent: :destroy
end

Swot.rb:

class Swot < ActiveRecord::Base
 belongs_to :sales_opportunity
 validates :swot_details, presence: true
 validates :sales_opportunity_id, presence: true
 enum swot_type: [:strength, :weakness, :opportunity, :threat]
 enum swot_importance: { minimal: 1, marginal: 2, noteworthy: 3, significant: 4, critical: 5 }
 validates :swot_importance, presence: true
end

Swot FactoryGirl spec:

FactoryGirl.define do
factory :swot do
    swot_importance             "minimal"
    swot_details                "Some boring details"
    swot_type                   "threat"

    trait :attached do
        association             :sales_opportunity, :with_user_id
    end
 end
end

Sales_Opportunity FactoryGirl spec:

FactoryGirl.define do
sequence(:opportunity_name) { |n| "Sales Oppotunity - #{n}" }

factory :sales_opportunity do
    user
    opportunity_name {generate(:opportunity_name)}
    close_date                  "2014/12/12"
    sale_value                  10000
    company_id                  7

    trait :with_user_id do
        user_id                     6
    end
end
end

Failing Rspec tests:

describe "when swot's parent sales opportunity is destroyed" do
    let(:swot) { FactoryGirl.create(:swot, :attached) }
    let(:sales_opportunity) { swot.sales_opportunity }

it "should destroy associated swots" do
    dswots = sales_opportunity.swots.to_a
    byebug
    sales_opportunity.destroy
    expect(dswots).not_to be_empty
    dswots.each do |dswot|
    expect(Swot.where(id: dswot.id)).to be_empty
  end
end
  end

Output from the console (byebug) when logging swot:

#<Swot id: 13, swot_type: 3, swot_importance: 1, sales_opportunity_id: 564, swot_details: "Some boring details", created_at: "2015-07-27 10:57:23", updated_at: "2015-07-27 10:57:23">

Output from the console when logging sales_opportunity:

#<SalesOpportunity id: 564, close_date: "2014-12-12 00:00:00", user_id: 6, created_at: "2015-07-27 10:57:23", updated_at: "2015-07-27 10:57:23", pipeline_status: 0, opportunity_name: "Sales Oppotunity - 4", company_id: 7, sale_value: #<BigDecimal:7fe9ffd25078,'0.1E5',9(27)>, swot_score: 0>

Output for sales_opportunity.swots.count:

(byebug) sales_opportunity.swots.count
 1

Output for sales_opportunity.swots:

(byebug) sales_opportunity.swots
#<ActiveRecord::Associations::CollectionProxy []>

I think I've included all the known info. The Rspec tests, FactoryGirl factories and setup between sales_opportunities and Swots/Timeline_Events is exactly the same - yet the Rspec tests pass for Timeline_Events and the collection_proxy works for those (so as far as I can tell, the code is identical):

Timeline_Event Factory:

FactoryGirl.define do
factory :timeline_event do
    activity                    "Some activity"
    due_date                    "2014/11/11"

    trait :attached do
        association             :sales_opportunity, :with_user_id
    end
end
end

Working Rspec tests:

describe "when sales opportunity is destroyed for timeline event" do
    let(:timeline_event) { FactoryGirl.create(:timeline_event, :attached) }
    let(:sales_opportunity) { timeline_event.sales_opportunity }

it "should destroy associated timeline events" do
    timeline_events = sales_opportunity.timeline_events.to_a
    sales_opportunity.destroy
    expect(timeline_events).not_to be_empty
    timeline_events.each do |event|
    expect(TimelineEvent.where(id: event.id)).to be_empty
  end
end
end

Timeline_Event.rb:

class TimelineEvent < ActiveRecord::Base
 belongs_to :sales_opportunity
 validates :activity, presence: true 
 validates :due_date, presence: true
 validates :sales_opportunity_id, presence: true
end

When running byebug in the same place here I get an array including the Timeline_Event.

Can anyone help me understand what's going wrong in my code?

Thanks.