Fix bug #10951.

The Buffer member for the remembered definition_ was not being set.

(cherry picked from commit f130f7713f)

src/mathed/MathData.h

@@ -171,6 +171,8 @@ public:
 	void updateMacros(Cursor * cur, MacroContext const & mc, UpdateType);
 	///
 	void updateBuffer(ParIterator const &, UpdateType);
+	///
+	void setBuffer(Buffer & b) { buffer_ = &b; }
 
 protected:
 	/// cached values for super/subscript placement

src/mathed/MathMacro.cpp

@@ -1180,4 +1180,10 @@ void MathMacro::completionPosAndDim(Cursor const & cur, int & x, int & y,
 }
 
 
+void MathMacro::setBuffer(Buffer & buffer)
+{
+	d->definition_.setBuffer(buffer);
+	InsetMathNest::setBuffer(buffer);
+}
+
 } // namespace lyx

src/mathed/MathMacro.h

@@ -129,6 +129,8 @@ public:
 	size_t appetite() const;
 	///
 	InsetCode lyxCode() const { return MATH_MACRO_CODE; }
+	/// Override so as to set Buffer for defnition_ member, too.
+	void setBuffer(Buffer &);
 
 protected:
 	friend class MathData;