diff --git a/app/models/competition.rb b/app/models/competition.rb
index ec5b021a14d..63e561368d0 100644
--- a/app/models/competition.rb
+++ b/app/models/competition.rb
@@ -643,9 +643,9 @@ def user_can_pre_register?(user)
     delegates.include?(user) || trainee_delegates.include?(user) || organizers.include?(user)
   end
 
-  attr_accessor :being_cloned_from_id
+  attr_accessor :being_cloned_from_id, :being_cloned_from_cache
   def being_cloned_from
-    Competition.find_by(id: being_cloned_from_id)
+    @being_cloned_from_cache ||= Competition.find_by(id: being_cloned_from_id)
   end
 
   def build_clone
@@ -709,7 +709,7 @@ def build_clone
     # Clone competition tabs.
     if clone_tabs
       being_cloned_from&.tabs&.each do |tab|
-        tabs.create(tab.attributes.slice(*CompetitionTab::CLONEABLE_ATTRIBUTES))
+        tabs.create!(tab.attributes.slice(*CompetitionTab::CLONEABLE_ATTRIBUTES))
       end
     end
   end
@@ -2449,7 +2449,13 @@ def to_form_data
   # It is quite uncool that we have to duplicate the internal form_data formatting like this
   # but as long as we let our backend handle the complete error validation we literally have no other choice
   def form_errors
-    return {} if self.valid?
+    self_valid = self.valid?
+    # If we're cloning, we also need to check the parent's associations.
+    #   Otherwise, the user may be surprised by a silent fail if some tabs/venues/schedules
+    #   of the parent are invalid. (This can happen if we introduce new validations on old data)
+    self_valid &= being_cloned_from&.tabs&.all?(&:valid?) if being_cloned_from_id.present?
+
+    return {} if self_valid
 
     {
       # for historic reasons, we keep 'name' errors listed under ID. Don't ask.
@@ -2542,7 +2548,7 @@ def form_errors
       },
       "cloning" => {
         "fromId" => errors[:being_cloned_from_id],
-        "cloneTabs" => errors[:clone_tabs],
+        "cloneTabs" => being_cloned_from_id.present? ? being_cloned_from&.association_errors(:tabs) : errors[:clone_tabs],
       },
       "other" => {
         "competitionEvents" => errors[:competition_events],
@@ -2550,6 +2556,10 @@ def form_errors
     }
   end
 
+  def association_errors(association_name)
+    self.public_send(association_name).map(&:errors).flat_map(&:to_a)
+  end
+
   def set_form_data(form_data, current_user)
     JSON::Validator.validate!(Competition.form_data_json_schema, form_data)
 
diff --git a/app/models/competition_tab.rb b/app/models/competition_tab.rb
index ea9a8d77647..4d97a728d2f 100644
--- a/app/models/competition_tab.rb
+++ b/app/models/competition_tab.rb
@@ -34,6 +34,16 @@ def slug
     competition.tabs.where("display_order > ?", display_order).update_all("display_order = display_order - 1")
   end
 
+  validate :verify_if_full_urls
+  private def verify_if_full_urls
+    content.scan(/\[(.*?)\]\((.*?)\)/).any? do |match|
+      url = match[1]
+      unless url.starts_with?('http://', 'https://')
+        errors.add(:content, I18n.t('competitions.errors.not_full_url', url: url))
+      end
+    end
+  end
+
   def reorder(direction)
     current_display_order = display_order
     other_display_order = display_order + (direction.to_s == "up" ? -1 : 1)
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 05c850e70fa..e811690d3a7 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -1963,6 +1963,7 @@ en:
       series_distance_km: "The competition is located too far away from %{competition}."
       series_distance_days: "The competition is scheduled too many days away from %{competition}."
       must_ask_about_guests_if_specifying_limit: "Must ask about guests if a guest limit is specified."
+      not_full_url: "You have a relative URL (%{url}) in the content. Please enter full URLs with prefix http:// or https://."
     new:
       create_competition: "Create competition"
       note_clone: "To clone an existing competition visit the information page for that competition and click the \"Clone\" link in the menu."
diff --git a/spec/models/competition_tab_spec.rb b/spec/models/competition_tab_spec.rb
index 2f0b72c14ec..0b346eba7f9 100644
--- a/spec/models/competition_tab_spec.rb
+++ b/spec/models/competition_tab_spec.rb
@@ -74,4 +74,18 @@
       expect(competition.tabs.to_a).to eq [tab1, tab2, tab3]
     end
   end
+
+  context "#verify_if_full_urls" do
+    let(:competition_tab) { FactoryBot.build(:competition_tab) }
+
+    it "doesn't allow relative URLs" do
+      competition_tab.update(content: "[Link](/relative)")
+      expect(competition_tab).to be_invalid
+    end
+
+    it "allows full URLs" do
+      competition_tab.update(content: "[Link](http://full)")
+      expect(competition_tab).to be_valid
+    end
+  end
 end