I noticed this happening with other items as well, not sure exactly why it occurs but perhaps the inventory limit on the crates is already maxed out thus you can't place more items in it. In the old days arma use to spill items out all over the ground that could not fit in the crate whenever someone attempted to put more in.

If this is the case then it be nice to have a weight indicator for crates so someone can determine if they are full or not (perhaps similar to how backpacks have a weight bar the fills up as they get more items in them).

Bring take-on helicopter model into game is what I suggest!

Yeah needs to be fixed, cant pick and choose backpacks in crates or clothing. Also I notice that backpacks do not STACK like ammo etc in the crates!