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That example from sebboh seemed to be because of stitching different sky tones, which isn't really an RX1 issue.
In-camera vignetting correction in a lot of cameras can be an issue, too. I leave mine off.
My apologies. I got confused.
Another thing to consider is that all RX1 (and A99/A77) raw files are compressed. They're essentially using the same compression as the old "cRAW" option on the A900, and it can be slightly lossy. If I remember correctly, the raws are compressed down into only 11 bits of tonal value, so that could cause this occasional issue when things are cranked in the raw converter.