diff --git a/product/ERP5/Tool/SolverTool.py b/product/ERP5/Tool/SolverTool.py
index a929658ef093079b601b8385526a5429f45cc368..6c3073ec6f0fa1cc52fd6141d411b70159e57c26 100644
--- a/product/ERP5/Tool/SolverTool.py
+++ b/product/ERP5/Tool/SolverTool.py
@@ -202,6 +202,9 @@ class SolverTool(BaseTool):
       test_property = 'quantity'
     application_value = movement
     try:
+      # XXX this way does not work correctly for category,
+      # eg. delivery_line.hasProperty('source') returns True even if it
+      # is only difined in its parent delivery.
       while not application_value.hasProperty(test_property):
         application_value = application_value.getParentValue()
     except AttributeError: