Items from from calendar page view when nid field hidden from display

I've come across an odd problem where if I don't display the node->nid, nodes will be dropped from the calendar page view.

Actual display of each calendar item is done via some PHP code in a Customfield; as I need to have some node types displayed as links and some not.

I've worked around it by adding a views theme override for the nid field as follows:

That works, but makes Views output horribly invalid HTML, so it's not ideal.