Most of Meilland codes ending with "sar" are climbing mutations. Only a few exceptions (Papa Meilland is one). So the likelihood of the unknown portion of the lineage of Polka is probably a climbing sport of a known rose. There have been known to be translation errors in Meilland codes over the decades, and Meilland has used Cl. Bettina (MEIpalsar) for other climbers, so its suspect to me at this point.

Edit: I did searching for no reason. The answer is right here in the US Patent:

"The female parent (i.e., the seed parent) was the product of the pollination of the Meipalsar variety (non-patented in the United States) and the Golden Showers variety (U.S. Plant Pat. No. 1,557). The male parent (i.e., the pollen parent) of the new variety was the Light Konigin Lucia variety (non-patented in the United States). The parentage of the new variety can be summarized as follows:

(Meipalsar×Golden Showers)×Licht Konigin Lucia."