2800319 Payment completion doesn't set BP open balance.

https://sourceforge.net/tracker/?func=detail&aid=2800319&group_id=176962&atid=879332
Use saveEx() instead of save() as recommended by Teo.

base/src/org/compiere/model/MPayment.java

@@ -1793,7 +1793,7 @@ public final class MPayment extends X_C_Payment
 				
 			bp.setTotalOpenBalance(newBalance);
 			bp.setSOCreditStatus();
-			bp.save();
+			bp.saveEx();
 		}		
 
 		//	Counter Doc