When I have my parkflyers Cessna 182 transmitter turned off, the servos still sometimes twithc from time to time on the way home from the flight field. Of course the battery is still in the plane, but is this a bad practice to leave it in the plane while on the way home or is there a problem with the system?

Yes, It's a good idea to disconnect the batt. before you turn off the trans. as without a stabilizing signal servos can run to the end of travel and damage the gears.