diff -up kcalc-4.10.5/kcalc_core.cpp.misc kcalc-4.10.5/kcalc_core.cpp

--- kcalc-4.10.5/kcalc_core.cpp.misc	2013-06-28 19:38:46.589913916 +0200

+++ kcalc-4.10.5/kcalc_core.cpp	2014-01-28 17:38:32.734620194 +0100

@@ -82,6 +82,9 @@ KNumber ExecAdd(const KNumber &left_op,

 }

 KNumber ExecSubtract(const KNumber &left_op, const KNumber &right_op) {

+    if (left_op.toQString() == right_op.toQString()) {

+      return KNumber::Zero;

+    }

     return left_op - right_op;

 }