So I went down to reunite my SK860 with its carriage. It performed beautifully. However, when I got it home, it started to play up again. Turns out if I put the left cam between 70L and 30L it "disappears" as far as the EC1 is concerned - so the pattern stops advancing. We only tried it out over 40 stitches, of course, so did not find the problem.
Hoping I can find someone local who can lend me something so that I can establish whether (a) the EC1 needs calibration or (b) it's actually the carriage at fault. If I recalibrate the EC1 I risk it not working with the SK840. Argh!
Alternatively I can just suck it up I guess and make sure I either knit items assymetrically (would cause problems with the long ribber comb) and/or make sure I travel to 70L whether I'm knitting that wide or not (can cause yarn take-up problems though).
In other news I made another Lilly wrap and a tuck lace scarf this weekend - both need some finishing. And the cameo vest re-crochet continues inexorably. Really need to get working on this stash!