Image does not show up when using 'setRowGroup'.

[sdsdsd]

Hello,
I am using Jxl to export to Excel. I am insering an image into a cell and then I use the 'sheet.setRowGroup' to group bunch of rows wheich also include the row that the image is in. When the Excel file opens up and I click on the + sign to upgroup the rows the image is missing! When I comment out the line of setRowGroup, then the image shows up but I need to be able to group the rows. Any idea why it's behaving this way? Thanks.

...
sheet.addCell(new Label(3, rowNum, "Image:", cellFormatGenaral));

byte[] ba = RenderUtils.filePathToByteArray("/images/stars/" + imageName + "_small.png");
WritableImage wi = new WritableImage(4, rowNum++, 1, 1, ba);
sheet.addImage(wi);

int lastGroupRow = rowNum-1;
sheet.setRowGroup(firstGroupRow, lastGroupRow, true);