I encountered this bug while playing the Sunglasses at Night featured contract: multiple guards on the map drop contraband whenever they pick it up. Here's a video to show what's wrong:
Interestingly, I could reliably reproduce this in the featured contract, but not in the main Icon mission. (Maybe I just wasn't standing in the right place.) In another thread, we had some discussion about this bug, and it seems that it occurs when you are located near or over a location where a guard is protecting a boundary between a trespassing zone and a non-trespassing zone. It might also affect how guards respond to distractions.
There's a five comment back-and-forth over here which might help you isolate the bug, IOI: http://www.hitmanforum.com/t/10-new-featured-contracts-5th-may/16375/61?u=quine