pewter bowl is missing “watertight” and “seals” tag.
From containers.json
compare
{
"id":"bowl_pewter",
"type":"CONTAINER",
"color":"light_cyan",
"symbol":")",
"name":"pewter bowl",
"category": "other",
"description":"A pewter bowl. Can be used as a container or as a tool. Holds 250 ml of liquid.",
"cutting":0,
"price": 400,
"weight":50,
"volume":1,
"bashing":0,
"to_hit":-1,
"material":"steel",
"contains":1,
"rigid": true
},
with
{
"id":"bowl_plastic",
"type":"CONTAINER",
"color":"light_cyan",
"symbol":")",
"name":"plastic bowl",
"category": "other",
"description":"A plastic bowl. Can be used as a container or as a tool. Holds 250 ml of liquid.",
"cutting":0,
"price": 100,
"weight":0,
"volume":1,
"bashing":0,
"to_hit":1,
"material":"plastic",
"contains":1,
"rigid": true,
"watertight": true,
"seals": true
},