I literally open the file as I received it, resize it, then copy and paste it into a new tile to create a seamless pattern.....and this happens.
How have I created this when I do not touch any settings anywhere and a few months ago I never had this problem it has started happening out of nowhere and I can not figure out how to make it stop.
Damien
You said '....I received it, resize it, then copy....'
Resizing to alter the number of pixels is re-sampling. Hence c.pfaffenbichler's comment on what happens when you resample using automatic on a layer that is not a background layer. If you have not seen it in the past either you were using a different resampling method or you were working with a background layer.
Dave