diff -r effc8c594683 tryton/health_services/health_services.py
--- a/tryton/health_services/health_services.py	Sun Dec 06 20:57:24 2015 -0600
+++ b/tryton/health_services/health_services.py	Mon Dec 07 18:47:35 2015 +0100
@@ -132,10 +132,9 @@
 
     @fields.depends('product', 'desc')
     def on_change_product(self, name=None):
-        res = {}
+        self.desc = None
         if self.product:
-            res['desc'] = self.product.name
-        return res
+            self.desc = self.product.name
 
     @classmethod
     def write(cls, lines, vals):