On Problems view, if you select "Show operational data -> Separately", the Operational data column will start to show a text *UNKNOWN* for triggers which do not have it defined at all.

This is unexpected, as basically the same(or very similar) message may be displayed for triggers which do have the "Operational data" defined.

This misleads a lot!
In zabbix logic we display *UNKNOWN* when we could not evaluate something, but there is nothing to evaluate and show the text.

So, I'm pretty sure we should display nothing for such triggers.
Or, at least, show different text, like "Undefined" or so.