diff -up KoboDeluxe-0.5.1/sound/a_midicon.c~ KoboDeluxe-0.5.1/sound/a_midicon.c
--- KoboDeluxe-0.5.1/sound/a_midicon.c~	2015-06-03 20:31:31.000000000 +0200
+++ KoboDeluxe-0.5.1/sound/a_midicon.c	2015-06-03 20:47:40.836311461 +0200
@@ -120,7 +120,8 @@ static inline void __press(unsigned ch,
 {
 	m[ch].next[key] = -1;
 	m[ch].prev[key] = m[ch].last;
-	m[ch].next[m[ch].last] = (char)key;
+	if (m[ch].last != -1)
+		m[ch].next[m[ch].last] = (char)key;
 	m[ch].last = (char)key;
 }