Hi lat9, it is set to true.
Configuration -> Customer Details -> State - Always display as pulldown? -> true
I have jscript on the create_account and all other address_book related pages to handle the English and Japanese with multilanguage, converting the codes to the corresponding language text (since in Zen Cart the state code use is as far as I am concerned a bug).

In OPC it seems like create_account is used the same as the original Zen Cart page, so my customizations work, but when it comes to editing addresses in the one_page_checkout page with the tpl_modules_{billing,shipping}_address template I presume the code is not available.
I'll have to check exactly what page the standard flow uses there and see what changes I have there.
I do not get any error either though, so there is no conflict as far as I can tell.