Steps to reproduce the issue

Create custom field extended from JFormFieldCheckboxes and add multiple options with disabled option in the middle of options.

Or test with XML:

<field name="test" type="checkboxes">
	<option value="1">1</option>
	<option value="2" disabled="true">2</option>
	<option value="3">3</option>
</field>

Expected result

Only 2nd checkbox is disabled.

Actual result

2nd and 3rd checkboxes are disabled.

System information (as much as possible)

As usual.

Additional comments

/layout/joomla/form/field/checkboxes.php:

The idea is to not use previous/field-specific 'disabled' attribute if there are more than 1 option.