It becomes something of a memory game at that point, doesn’t it?!

I managed to map a 21 probe Type II in “scanned planet” mode today, and gain the efficiency bonus - I’m not sure if that means I have a good spatial memory, or whether I am just too stubborn for my own good
Well, after a bit of a marathon session today, I am no closer to saying
what provokes it, but here are my observations which might be useful:
1: It isn’t linked to scanning the same body type. I have purposely gone and scanned two bodies of the same type one after the other, both as first bodies visited in system, and not. I have done this with MR, HMC, WW, Icy, and Rocky bodies. Although I have scanned GG, I didn’t do two consecutive body scans - though note that on one occasion all bodies had been fine up until I went to scan a Type II...
2: Scanning a WW doesn’t always provoke the bug for subsequent bodies.
3: When scanning, I never leave supercruise until all the bodies I am interested in are scanned - I don’t know if this is relevant, but thought it should be mentioned in case it turns out to be.
4: It doesn’t always happen in each system.
5: On one occasion, there was just a single body in the system; when I supercruised towards it to scan, it turned into the “already scanned” display.