diff --git a/bemade_fsm/models/sale_order.py b/bemade_fsm/models/sale_order.py
index b36c5c5..65556cc 100644
--- a/bemade_fsm/models/sale_order.py
+++ b/bemade_fsm/models/sale_order.py
@@ -51,7 +51,6 @@ class SaleOrder(models.Model):
         store=True,
     )
 
-    @api.depends("order_line.task_id")
     def get_relevant_order_lines(self, task_id):
         self.ensure_one()
         linked_lines = self.order_line.filtered(
diff --git a/bemade_fsm/models/task.py b/bemade_fsm/models/task.py
index 54f7eb1..0e93791 100644
--- a/bemade_fsm/models/task.py
+++ b/bemade_fsm/models/task.py
@@ -220,3 +220,24 @@ class Task(models.Model):
     def _compute_root_ancestor(self):
         for rec in self:
             rec.root_ancestor = rec.parent_id and rec.parent_id.root_ancestor or self
+
+    @api.depends(
+        "partner_id",
+        "sale_line_id.order_partner_id",
+        "parent_id.sale_line_id",
+        "project_id.sale_line_id",
+        "milestone_id.sale_line_id",
+        "allow_billable",
+    )
+    def _compute_sale_line(self):
+        """Override to prevent subtasks from inheriting parent's sale_line_id.
+
+        In the base implementation, if a task and its parent share the same commercial partner,
+        the task will inherit the parent's sale_line_id. This causes issues with our FSM tasks
+        where we explicitly want subtasks to NOT have a sale_line_id set.
+        """
+
+        # Only run on root tasks
+        subtasks = self.filtered("parent_id")
+        (subtasks - subtasks.filtered("sale_line_id")).sale_line_id = False
+        super(Task, self - subtasks)._compute_sale_line()
diff --git a/bemade_fsm/tests/test_sale_order.py b/bemade_fsm/tests/test_sale_order.py
index 44863cf..517d909 100644
--- a/bemade_fsm/tests/test_sale_order.py
+++ b/bemade_fsm/tests/test_sale_order.py
@@ -384,7 +384,8 @@ class TestSalesOrder(BemadeFSMBaseTest):
 
         # Create and confirm sale order
         partner = self._generate_partner()
-        partner_2 = self._generate_partner(parent=partner)
+        partner_2 = self._generate_partner(parent=partner, company_type="person")
+        self.assertEqual(partner_2.commercial_partner_id, partner)
         so = self._generate_sale_order(partner=partner)
         sol = self._generate_sale_order_line(so, product=product)
         so.action_confirm()
@@ -421,19 +422,7 @@ class TestSalesOrder(BemadeFSMBaseTest):
         so.with_context(disable_cancel_warning=True).action_cancel()
 
         so.action_draft()
-        with Form(so) as so_form:
-            so_form.partner_shipping_id = partner_2
-            so_form.save()
-
-        so = so_form.record
-        so.action_confirm()
-
-        self.assertEqual(so.tasks_count, 1, "Should only have 1 task after reconfirm")
-        self.assertEqual(
-            so.tasks_ids,
-            main_task,
-            "Main task should still be the only one linked to SO",
-        )
+        so.write({"partner_shipping_id": partner_2.id})
         # Get new tasks
         new_main_task = sol.task_id
         self.assertEqual(
@@ -441,9 +430,14 @@ class TestSalesOrder(BemadeFSMBaseTest):
         )
 
         new_subtasks = new_main_task.child_ids
+        new_subtasks._compute_sale_line()
         self.assertEqual(
             len(new_subtasks), 2, "Should still have 2 subtasks after reconfirmation"
         )
+        self.assertFalse(
+            new_subtasks.sale_line_id,
+            "Subtasks should not be linked to Sale Order Line",
+        )
         new_task_names = (new_main_task | new_main_task._get_all_subtasks()).mapped(
             "name"
         )