Not a bug. 52, 703, and 702 KB are very small sizes. It is normal and good that an exported file is larger than its inputs due to lossy compression. Please learn a little about digital video compression and how the editing process affects that.
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While lossy compression can help video be transmitted more rapidly and take up less space, this type of format suffers from generation loss. Over time if you continue to compress and decompress your file using lossy compression methods you will decrease the quality of your file over time.
Most video editors (at least any that offer multiple tracks and effects) must recompress. YouTube will also recompress to make the video streamable. With all of these generations of loss you want your export to be a little large to preserve quality. With that said, the export defaults (also Reset button or Default preset) will make something very similar to the YouTube preset but smaller and no quality loss. The YouTube preset was created to adhere to YouTube’s documented guidelines, but it accepts much more than what its guidelines suggest.