MicroPilot,
How uneven was the ground you were mowing when your "freewheeling" happened?
Here's the reason I ask... I've been rather surprised/disappointed at how little oscillation the front axle on my 2028 has. It's really not very nimble on uneven ground. As soon as one front wheel runs up on a bump, even in 4WD, it hits the axle stop, which takes weight off the one rear wheel and it loses traction. The only way to keep moving is to lock the rear axle(the pedal at your right heel) so both rear wheels pull together regardless of traction.
My guess in your situation is this...you hit an uneven spot with a front wheel which lifted one of your rear wheels, losing traction for the time it "freewheeled". This is just the reverse of losing traction while pulling uphill.
The fix is the same--lock the rear axle when you need full traction. You will go straight, of course, and will need to release the lock before turning.
Try this when you mow the same area again and see if it reduces the "pucker factor".
Lynn