Drupal 7 Form API Select element shows some emtpy values after migration

hi everyone, 

my partner has installed the development environent of our company in his PC. the installation was exactly the same i have on my machine ( IIS with exact configuracion, same php version with exact php.ini,  exact version of MariaDB, etc…) the only difference is that i have Windows 7 64bits and he has Windows 10 64bits.

the problem is that the select element in our custom forms ( with Form API) shows some black values on the machine with windows 10. Using print_r before return the $form element in the hook_form whe can see the array containing all the indexes and the values correctly.

here is an example capture of what its happening.

Example Capture

what can we do to solve this? 

thanks in advance!

Drupal version: 

Source: https://www.drupal.org/taxonomy/term/4/feed