Textures show up as missing

Textures in resourcen packs, which were added (not edited existing ones), don't load in-game, despite correct path in the JSON file of the block model.

also it's not possible anymore to map existing textures, which aren't part of the original block to it.

for expample the upper part of an oak door:

oak_door_top.json

{
"textures":

{ "particle": "#top", +"anvil_base": "blocks/anvil",+ "texture": "block/oak_door_top" }

,
"elements": [ 
{
"from": [ -0.5, 10, -0.5 ],
"to": [ 3.5, 12, 1 ],
"shade": false,
"faces":

{ "down":

{ "uv": [ 16, 1, 12.5, 0 ], "texture": "#anvil_base" }

,

......

..

The anvil texture is shown as missing in the game.