It seems like some items, after you drop them to the ground,
crumble:

<590 HP  756 MA  479 MV || 5 AM civilized> n
An Eerie Cavern
 
[Exits: east south]

<590 HP  756 MA  475 MV || 5 AM civilized> drop knapsack
You drop a cowhide knapsack.
..........
You get a cowhide knapsack.

<431 HP  762 MA  463 MV || 7 AM civilized> 
<someone> has arrived.

<431 HP  762 MA  463 MV || 7 AM civilized> wear all
You wear a cowhide knapsack about your body.
....
<431 HP  762 MA  463 MV || 7 AM civilized> l
An Eerie Cavern
......
<368 HP  733 MA  445 MV || 8 AM civilized> 
<someone> leaves east.
You follow <someone> east.
The Outer Veil
 
[Exits: north east south west]
<someone> is here.
A cowhide knapsack crumbles into dust.

<368 HP  733 MA  441 MV || 8 AM civilized> 
<someone> leaves east.
You follow <someone> east.
The Outer Veil
 
------------------------
Not all items crumble - along with knapsack, I dropped all my
equipment - and it didn't crumble.