Prevent too large <backup> values in PartStaffExporter

music21/musicxml/partStaffExporter.py

@@ -743,7 +743,12 @@ def moveMeasureContents(measure: Element, otherMeasure: Element, staffNumber: in
 
         # Create <backup>
         amountToBackup: int = 0
-        for dur in otherMeasure.findall('note/duration'):
+        for note in otherMeasure.findall('note'):
+            if note.find('chord') is not None:
+                continue
+            dur = note.find('duration')
+            if dur is None:
+                continue
             backupDurText = dur.text
             if backupDurText is not None:
                 amountToBackup += int(backupDurText)
@@ -1067,6 +1072,23 @@ def testMeterChanges(self):
         root = self.getET(s)
         self.assertEqual(len(root.findall('part/measure/attributes/time')), 3)
 
+    def testBackupAmount(self):
+        '''Regression test for chord members causing too-large backup amounts.'''
+        from music21 import chord
+        from music21 import defaults
+        from music21 import layout
+
+        ps1 = stream.PartStaff(chord.Chord("C E G"))
+        ps2 = stream.PartStaff(chord.Chord("D F A"))
+        sg = layout.StaffGroup([ps1, ps2])
+        s = stream.Score([sg, ps1, ps2])
+
+        root = self.getET(s)
+        self.assertEqual(
+            root.findall('part/measure/backup/duration')[0].text,
+            str(defaults.divisionsPerQuarter)
+        )
+
 
 if __name__ == '__main__':
     import music21