I noticed this in a job I am running now. In the outer blue border the offset fill is leaving an unburnt line down the centre of each side and at places along the curve. My normal setting is a line interval of 0.1 - 0.15mm. I have attached pictures at 0.085 (300 dpi that shows it getting less noticeable but still there. I need to go to 400 dpi to get rid of them. The preview is showing what happens in real life. The 400 dpi is about 4 mins slower than the 254dpi setting, but still 10 mins quicker than just using fill with flood fill set on. Is this behaviour you would expect?