CellTable rebuilding rows unnecessarily

I have found an interesting issue, and I am wondering if I am misusing or overlooking something. I have a large CellTable that is vertically scrollable. I want to show all the rows at once instead of traditional pagination. So at the bottom of my table I have a row that the user can click to load 50 more rows. I have provided the table with a custom table builder (setTableBuilder(new Builder());). When the user clicks "load more" I query the data, add to the ListDataProvider and call table.setVisibleRange(0, dataProvider.getList().size());. 

I put a log statement in the 

@Override

public void buildRowImpl(Object rowValue, int absRowIndex) {

}

method to see when it was building rows. I notice that it would build 0-dataProvider.getList().size() (all the rows), then it would build oldLength-dataProvider.getList().size() (the new rows). For instance, if I have 100 rows and then load 50 more it would build 0-150, and then rebuild 100-50. What I want is for it to only build the new rows, obviously. 

So I start debugging to see why it is rebuilding the whole table each time. What I found was in com.google.gwt.user.cellview.client.HasDataPresenter<T> it would set the "redrawRequired" flag to true at line 1325:

else if (range1 == null && range0 != null && range0.getStart() == pageStart

        && (replaceDiff >= oldRowDataCount || replaceDiff > oldPageSize)) {

      // Redraw if the new data completely overlaps the old data.

 redrawRequired = true;

}

So my question is why does it think that the new data completely overlaps the old data?

Am I using something incorrectly, is there a better way? This gets to be quite a slow down when it has to redraw thousands of rows that don't need to be redrawn.

Thanks,

Will

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