This is typical in cases where the customer has not changed the filter in over a year, or has excessively grainy water. The reason your boss has not seen anything like this in his 4o years is because Amana and Maytag only went with this type of filtration system in 2001. The system uses the new Guest fittings and has an automatic shutoff valve built into the filter head so that when the filter is removed, no water can pass thru the system unless the blue bypass plug is in place. (It pays to save these bypass plugs in case you need one in the field)
Advise your customer to change this filter every six months, not yearly. If they begin to experience hollow ice cubes or the fountain will not fill 8 ounces of water in 15 seconds, they may have pressure issues not related to the refrigerator. Remember that Amana and Maytag refrigerators may not be used on an R/O system.