Cannot override com_content/models/article

[LivioCavallo]

The plugin was great so far! Today I found a problem using Joomla! 3.4.4 frontend editing feature.

1. simulate an override to components/com_content/models/article.php (site), simply copying it into code/com_content/models/article.php OR 1bis) simulate an override to components/com_content/models/article.php (site), simply copying it into template_name/code/com-content/models/article.php ;
2. from the frontend open an article, then edit it from the frontend: you'll get a blank page!

Some ideas to solve it? I bypassed the error doing a core-hack to that file... instead of an override...

[LivioCavallo]

Any ideas?