This isn't often noticed by the beekeeper
"Silent robbing" is a term that was used in old beekeeping books and by the older beekeepers, but is very rarely mentioned nowadays. This is probably because beekeepers aren't as observant as they once were, so don't notice it. I think silent robbing happens more than many beekeepers realise.
You can sometimes see silent robbing late in the evening, when flying in most colonies is coming to an end. If you see two colonies that are more active than the others, watch carefully and you may see bees flying out of one hive and into another unopposed. The robbed colony may be quite strong and the entrance small. For some reason silent robbers don't behave like "normal" robbers, who will dart about in front of the entrance before trying to enter. They simply enter as if they were a member of the robbed hive. This suggests to me the scent may be very similar in both colonies, allowing one to let the other in without challenge.
Normal robbing usually happens when there is a nectar dearth, very often when a nectar flow stops abruptly, but I have often seen silent robbing in the evening when there is nectar coming in. Because bees that are robbing silently don't behave like bees that are robbing normally and there is usually a great amount of activity when there is nectar coming in, it is difficult to tell if silent robbing continues throughout the day. I'm not aware of any research to consult, so we will have to rely on individual observation.
I'm not aware of any cure for silent robbing, but all the honey is yours, so does it really matter which hive you harvest it from? There are only two problems that are likely to be caused by silent robbing. Firstly there is the possibility of spreading foul brood, but if you check your colonies regularly that shouldn't be a problem, secondly you may think the robbers are better honey producers than the robbed colony, which may encourage you to breed from them.