I contacted Luxman. Here is their response and explanation:
IR remote control works by sending out a certain amount of infrared light that symbolizes certain binary codes. It is possible (and often does occur) that certain sequences are close enough to others so as to cause misinterpretation by adjacent IR receivers. While not exactly the same, imagine that the code for something was 2222 and the adjacent device was looking for 222... it is possible for the second device to interpret the first three 2's of the first code as its' own 222 code. There would be no way to keep this from happening, except by covering up one of the receivers. We see this from time to time, usually with older units (>10 years old) placed near other newer units.
It makes sense....I am not sure using a universal remote would prevent this from happening.