Yep definitely need to run in float position.

Remote valve could have a leak in it somewhere allowing small amount of oil flow that is causing the markers to creep up. 

Another alternative if you have 2 remotes on the tractor and your markers are tied into the lift cylinder on the planter is to pull the marker hose off the lift cylinder and run it to the second remote with just 1 hose. I did this on my early 7200 to get independent marker control for crossing waterways.

Without it you would get to the water way, raise planter, cross waterway,stop on other side, lower planter wrong marker goes down, raise again and lower to get correct marker then go.

Now I come to waterway raise planter, correct marker stays down, cross waterway and lower planter on other side all without stopping.