If a vine is on the bottom of a block and you break the block, the vine briefly flashes a 8x8 cube missing texture block before disappearing.
Linked issues
Attachments
Comments 7
Also when you /setblock vines, without specifying a data value, it permanently displays this weird cube. It only goes away when the vine block goes away, which is possible by updating it.
I don't think there would be a specific model for that, so I think you were right when you said it was a missing model/texture sort of block.
I've been playing with block models, and it seems that is the "missing model" model.
The basic problem is vines don't know what model to use when the supporting block above is destroyed.