When using a ListSubModel in a chosenbox, the chosenbox _renderByServer is set to true.
This cause the _fixDisplay function on the chosenbox to go into:

this._fixEmptyDisplay(

{ showBlank: !this.$n("sel").firstChild }

)

This in turn will remove the "empty-creatable" class from the chosenbox if the text typed in the search field did not return at least one possible result (included hidden result already selected). as the value of this.$n("sel").firstChild will be: null

In turn, this cause the doEnterPressed function to not send the onSearch event at:
if ((c = this.$n("empty")) && jq(c).hasClass(this.$s("empty-creatable"))) {
this._fireOnSearch(this.$n("inp").value);
if (this._open) {
this.setOpen(false,

{ sendOnOpen: true }

)
}