The List Size reverts to 5 after every apply or save of any kind. Setting it to zero should make the parameter a drop down but the List Size is always reverts back to 5. Cannot set the List Size to any other value without it reverting back to 5 on Save.
The <listSize>0</listSize> can be set manually in the config.xml for the jobs and a restart of Jenkins will make the value stick until the job is edited for any reason, including non-Git Branches plugin related changes. It will revert back to 5 with any Save.
List Git Branches Parameter Version: 0.0.9