I have seen this before as well. But only in front of glass doors where the heat seems to have caused the chemicals the rubber to bleed into the flooring.
I don't believe anything short of patching it would do the trick. I have not heard of this happening to a floor with a rug without a rubber backing or a rubber non skid pad.
ps..I think a real floor should be determind by the person whose shoes are walking on it and spending the real money for it.
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