Uh...

1. Log in.
2. Find a backpack or a tent loaded with stuff.
3. Hit tab. Note that it is either empty, or haphazardly loaded with a few things in scattered positions.
4. Drop something inside (or pull something out).
5. See everything magically appear.

Screenshots here:

Before Inventory appears
http://steamcommunity.com/sharedfiles/filedetails/?id=355036545

After Inventory appears
http://steamcommunity.com/sharedfiles/filedetails/?id=355036573

I don't recall it doing this in previous versions, or if it did, I never noticed it before. However, there is a good reason for this if so:

Only recently (after the last update) my friend and I found 2 big military tents. We weren't paying any attention to unequipped containers before then, and first noticed it with the tents, when I freaked out, thinking everything was stolen. Then it appeared after dropping something inside.

Since we've been testing everything about tents, including the decay rates, we paid close attention to the backpacks dropped on the floor within. Sure enough, they exhibited the same properties (for both of us)

We thought perhaps this was a bug with a container being inside an already buggy container (backpack inside a tent), but no, the behavior is easily enough found outside the tent and in other structures. But since we only just now started looking for it, we have no idea if it was happening previously in old versions