Opening .WK4 files in OOoCalc

I did a search in the forums using 'wk4' as the search term with 0 results, so here's the question:

I recently obtained for work some small (under 200kb) .WK4 files (from an old Lotus 1-2-3-based application) and tried to open them in a copy of OOo Portable. When using the 'Open' dialog, I get a Writer window with garbage. When using drag-n-drop, the error message is 'unknown Lotus-1-2-3 file format'. So, I dug up a machine with MS Excel on it and excel read the files without problem. Any suggestions about what is happening? I guess I could use Excel to convert the files to Excel format and use the converted copy, but that seems dumb (trying to get away from MS by using MS).