The issue with carrying anything on the front is where the load is with relation to the front wheel's center of gravity AND the axis of the turn vs the center of gravity of the bike under load.
That is, if the load's center of gravity is out front of the wheel's center/hub, then you are going to find it more difficult to turn/control the wheel. Picture it like this - take a broom, hold it at arm's length heavy end away from you.
Now swing it up and down... Reverse it and do the same.. Feel the difference? Try swinging the weight with the weighted end of the broom close to and away from you(this simulates turning the wheel, beleive it or not). Feel THAT difference?
What you noticed was the effect of leverage with respect to location placement of the weight. (I hated physics in school so I don't remember the terms/formulas exactly.. but you should be able to get the idea).
The closer the load's weight is to the wheel's center of gravity, the easier it is to turn the wheel. IF the load's weight is behind the wheel, it's just as hard to turn the wheel as if it was in front - BUT the bike will still balance when leaned over while rolling because you moved the weight towards the BIKE's center of gravity.

While the weight of the load itself is transfered to the wheel thru the rack and mount points, it's still got mass where it sits - that's what may be throwing you off.

So, either center the load weight over the hub itself or slightly rearward if you find that you can handle it/prefer it that way.