I'm testing the MaxItems limit set through itemdesc.cfg on a container. I can actually insert more than the limit using bags full of items - e.g. I can insert 3 bags with 300 items each in a container with 500 MaxItems set.
I've found this thread viewtopic.php?f=42&t=3058&p=15306&hilit=maxitems#p15306 from quite a few years ago, where Turley says

...After this update:
every container can hold up to 3200 items (fixed core value)
if you add something to a subcontainer core checks for weight and itemcount inside the subcontainer, for every parentcontainer it checks for itemdesc.maxweight

Is it still correct? Does the MaxItems value is ignored for items in subcontainers?

Anyone?

If I remember correctly a bag containing items dropped in a container counts as one item against max items for the container in which the bag is placed. However, the weight of the bag and the items in the bag do count against the max weight of the parent container.

One thing I can't remember is if a stack of say ten items counts as one item or ten items when dropped into a container.

I confirm what Turley posted some year ago.
Items in a bag placed in a container doesn't count for the MaxItems of the container, just for its weight.

That's what I thought but it's been awhile since I checked on it.