Follow this steps to reproduce it (on a clean Jenkins):

1. Create a freestyle job
2. Add a batch task
3. Add a post-build step "Invoke batch tasks"
4. Set the name of the current job in the "Project" field and press tab (remove the focus on "Project" generally)
5. The batch tasks drop-down is not loaded

Workaround: save the job and go to configure again, then the drop-down is filled correctly.