NOT specific, but the temperature needs to be controlled, So depending on settings, The m/c might be overriding your slow request, i.e slow is not appropiate to the media being fed. Is the m/c working ok, i.e the project is correctly laminated? Thicker, heavy gauge lamination, would need a slow speed, for the heat to get through, a thinner would not, and a slow speed then, would damage the work. IF the unit is doing its job, I would not worry about it. If it not doing its job, problem with control, but on two units??
SD, June 2011