That is common when maneuvering due to side loads on the tires. If you have room, try pulling the trailer straight ahead a truck length or two and then straight back. See if that equalizes things.
Grease on the backside of the tire could mean a seal failure and possibly grease on the brakes. There shouldn't be grease on the frontside either, but it probably isn't a serious problem. Have you cleaned it off to see if it happens again?
Sherm & Terry w/rescues Steve (std Poodle) & Eydie (min Schnauzer)
2015 Jay Flight 27RLS (Camped: 102 nights 2015, 90 nights 2016)
2006 Ford F350 6.0 PSD, Lariat, 4WD, CC, LB, SRW, auto., Camper pkg.