Reproducible: always
Steps to reproduce:
0. Turn on Narrator
1. Download jar with accessibility test samples from https://wiki.se.oracle.com/download/attachments/46472587/Hello.jar
2. Execute ChoiceBox demo by java -cp Hello.jar hello.HelloChoiceBox
3. Try to expand it using F4, space or ctrl-down
Expected result: ChoiceBox expanded
Actual result:
Nothing happens on F4 or ctrl-down
Can be expanded with space for one time, doesn't react when collapsing it and trying to expand again.

Combobox without default selected element can't be expanded even once.