Validation problems if other fields are hidden

I use Entity Reference View Widget on the form, where some other fields are hidden in hook_form_alter using following way:

$form['field_name'] ['#access'] = FALSE;

Clicking submit button, user sees validation errors, that such fileds are empty. If Entity Reference View Widget is disabled, then no such error happens. I tried to reproduce it with 7.x-1.x-dev, but have other warning messages:

Warning: date_offset_get() expects parameter 1 to be DateTime, null given in date_combo_validate() (line 564 of /var/www/site/sites/all/modules/contrib/date/date_elements.inc).

Steps to reproduce this issue:
* Install and enable Entity Reference View Widget for nodes/entities.
* Add reference field to the node/entity.
* Add the Date field to the node/entity and make it required.
* Alter node/entity form and hide date field using ['#access'] = FALSE;.
* When adding node/entity, select referenced nodes/entities (THIS IS IMPORTANT STEP).
* Click submit button.

See error messages or warnings depending on the version of module is used.