Error with "Currency restrictions" in my custom Payment Module

[superuser2017]

Hi.
I developing a payment module. I got a error with the option "Currency restrictions"
(you can see that in the option: Modules and services > Payment).
I dont see the checkbox. But when i install my module for first time i can see and use that. But later of 2 or 3 refresh of the page, i cannon see anymore. But if i edit the code of the module (for example adding a blank lines that dont make a changes in PHP) that work fine for 2 or 3 petitions of the page.
I attach a screenshot and the code of the module (is very little code but the error can be replicated with this code).
I using Prestashop 1.6.1.11.

examplepago.zip