During one of my antenna experiments I took 2 Baofeng UV-5R radios with me. One has firmware version BFB231, the other BFB251. While listening to some signals I noticed a sudden decrease in volume when both radios were in close proximity to each other.
Interesting. The audio coming out of both radios was not in phase, which caused them to cancel each other out almost completely. A strange experience, but easy to explain. Every change in software can cause a DSP or SDR design to process the signals either slower or faster. In this particular case the combination of both UV-5Rs acted as a noise canceling system, similar to the image below.