Well, sounds like you have a good cold section in the dehumidifier-- that is good!-- But I agree-- we don't want water condensing on the surface-- and we surely don't need it turning to ice!
A couple questions to help us get to the next level of trouble shooting this problem:
1.) How cold is the room you are running the dehumidifier in?
(Obviously-- the warmer a room is, the easier to remove moisture--
the colder the room, the easier to drop the air temperature well below the freezing point-- making ice.)

2.) Have the air filters been cleaned/changed recently?
A dehumidifier needs a steady fast moving supply of air across its whole condenser/evaporator surface, in order to remove the maximum amount of water from the air, and not freeze up. (I would winder if something isn't blocking the flow of air toward the top of the coil?-- so that the coil in that area is going well below freezing temperatures, and thus allowing water (or ICE!) to develop near the top of the coil?-- Can you check air flow for us?

3.) You have suggested a good solution,-- especially if the above problems can not be easily corrected: Turn off the unit every few hours, and allow the warmth of the room, to defrost the coil....
In fact-- just to make sure that the air flow is not being restricted by ice deep within the coil-- let it stay off over night-- or bring the dehumidifier into a much warmer room, to make sure no ice is still blocking air flow deep within the coil..

Let us know what you learn about air flow, and get back with us-- THen maybe we need to take the trouble shooting deeper insicde the device.

I hope this helps-- MB