@mkly Just debugger the code with the version that's now under master.
If we call populateParentIDArray with $cID = '1' I get this call stack:
```php
populateParentIDArray called with $cID = '1'
Page::getCollectionParentIDFromChildID('1') returns '0', assigned to $cParentID;
($cParentID > -1) is true
	'0' is added to the array $this->cParentIDArray
	populateParentIDArray called with $cID = '0'
		Page::getCollectionParentIDFromChildID('0') returns null, assigned to $cParentID;
		($cParentID > -1) is false
`
As result, $this->cParentIDArray is array('0')