Program: 152049
Project: 152049
Buggy source:
@Override public void layout(){
  Insets insets=getInsets();
  int twidth=getWidth() - insets.getHorizontal();
  int theight=getHeight() - insets.getVertical();
  int gap=((GroupLayout)getLayoutManager()).getGap();
  int totheight=0;
  int snapheight=0;
  for (  Entry<V,C> entry : _values) {
    if (entry.height < 0) {
      if (entry.component == null) {
        entry.component=createComponent(entry.value);
      }
      boolean remove=false;
      if (!entry.component.isAdded()) {
        add(entry.component);
        remove=true;
      }
      entry.height=entry.component.getPreferredSize(twidth,0).height;
      if (remove) {
        remove(entry.component);
      }
    }
    if (entry.value == _snapValue) {
      snapheight=totheight;
    }
    totheight+=entry.height;
  }
  if (_values.size() > 1) {
    totheight+=(gap * _values.size() - 1);
  }
  int extent=Math.min(theight,totheight);
  int value=_model.getValue();
  if (_snap) {
    value=totheight - extent;
    _snap=false;
  }
 else   if (_snapValue != null) {
    _snapValue=null;
    value=Math.min(totheight - extent,snapheight);
  }
  if (extent != _model.getExtent() || totheight != _model.getMaximum()) {
    _model.setRange(0,value,extent,totheight);
  }
  _offset=_model.getValue();
  int compIx=0;
  for (int ii=0; ii < _values.size(); ii++) {
    Entry<V,C> entry=_values.get(ii);
    if (_offset < entry.height) {
      compIx=ii;
      break;
    }
    _offset-=(entry.height + gap);
    if (entry.component != null) {
      if (entry.component.isAdded()) {
        remove(entry.component);
      }
      entry.component=null;
    }
  }
  extent+=_offset;
  int topIx=compIx;
  while (compIx < _values.size() && extent > 0) {
    Entry<V,C> entry=_values.get(compIx);
    if (entry.component == null) {
      entry.component=createComponent(entry.value);
    }
    if (!entry.component.isAdded()) {
      add(compIx - topIx,entry.component);
    }
    extent-=(entry.height + gap);
    compIx++;
  }
  while (compIx < _values.size()) {
    Entry<V,C> entry=_values.get(compIx);
    if (entry.component != null) {
      if (entry.component.isAdded()) {
        remove(entry.component);
      }
      entry.component=null;
    }
    compIx++;
  }
  super.layout();
}

Fixed version (ground truth):
@Override public void layout(){
  Insets insets=getInsets();
  int twidth=getWidth() - insets.getHorizontal();
  int theight=getHeight() - insets.getVertical();
  int gap=((GroupLayout)getLayoutManager()).getGap();
  int totheight=0;
  int snapheight=0;
  for (int ii=0, nn=_values.size(); ii < nn; ii++) {
    Entry<V,C> entry=_values.get(ii);
    if (entry.height < 0) {
      if (entry.component == null) {
        entry.component=createComponent(entry.value);
      }
      boolean remove=false;
      if (!entry.component.isAdded()) {
        add(entry.component);
        remove=true;
      }
      entry.height=entry.component.getPreferredSize(twidth,0).height;
      if (remove) {
        remove(entry.component);
      }
    }
    if (entry.value == _snapValue) {
      snapheight=totheight + gap * ii;
    }
    totheight+=entry.height;
  }
  if (_values.size() > 1) {
    totheight+=(gap * _values.size() - 1);
  }
  int extent=Math.min(theight,totheight);
  int value=_model.getValue();
  if (_snap) {
    value=totheight - extent;
    _snap=false;
  }
 else   if (_snapValue != null) {
    _snapValue=null;
    value=Math.min(totheight - extent,snapheight);
    _model.setValue(value);
  }
  if (extent != _model.getExtent() || totheight != _model.getMaximum()) {
    _model.setRange(0,value,extent,totheight);
  }
  _offset=_model.getValue();
  int compIx=0;
  for (int ii=0; ii < _values.size(); ii++) {
    Entry<V,C> entry=_values.get(ii);
    if (_offset < entry.height) {
      compIx=ii;
      break;
    }
    _offset-=(entry.height + gap);
    if (entry.component != null) {
      if (entry.component.isAdded()) {
        remove(entry.component);
      }
      entry.component=null;
    }
  }
  extent+=_offset;
  int topIx=compIx;
  while (compIx < _values.size() && extent > 0) {
    Entry<V,C> entry=_values.get(compIx);
    if (entry.component == null) {
      entry.component=createComponent(entry.value);
    }
    if (!entry.component.isAdded()) {
      add(compIx - topIx,entry.component);
    }
    extent-=(entry.height + gap);
    compIx++;
  }
  while (compIx < _values.size()) {
    Entry<V,C> entry=_values.get(compIx);
    if (entry.component != null) {
      if (entry.component.isAdded()) {
        remove(entry.component);
      }
      entry.component=null;
    }
    compIx++;
  }
  super.layout();
}