Thanks Rex!
Another day, another repro
Here the images were stacked using intersect mode in DSS. Also I found an issue with my bias frames...I had divided the bias frames across the appropriate light groups, but for some unfathomable reason DSS is refusing to load the bias frames for one of the image groups (and I know the files are fine as they work OK in a stack of the lights and biases by themselves). It's almost like it doesn't want to load any more files
anyhow, I cheated and divided the bias set from another group and it allowed me to add them. Weird.
Anyhow, the end result from the intersection stack isn't so awkwardly framed IMO, I can live with it
This has been tretched to bring out the nebulosity and the colours almost brought themselves out, maybe just a little teasing. There's a tiny green problem on the RHS of the image and I'm not sure why. I don't remember seeing green stars, but maybe it's some green-channel shifting artefact from stacking. Dunno.