Hi. I had 2 cartographers. My opponent stole control of one. I then attacked his controlled with mine, and when the proc ability went off; he got 3 lands and I got 1. Should have been 8 lands, 4 for him and 4 for me.
I posted this via your bug form btw.
Did you take a screenshot? If you did, mind sharing it here? Sometimes the cartographer acts a bit weird (wont build land next to your orb for example) 
No, but I will in future. It was adjacent to my right energy source though.
