I tried this out myself and had the same problem exporting to the Lotus 1-2-3 format. I also found the solution. Make sure to specify the filename when exporting to 1-2-3 format including the extension .wk4. I found the solution using http://www.support.lotus.com . Try searching for 802564910029BEB5.
Dig Deeper on Domino Resources - Part 5
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