There are two ways to use conditional formatting:
The second option works on any table row, no matter what the content is (so you could show or hide your reference selector for example).
The first option, the one you want to use, doesn't seem to work correctly on all input widgets: simple text boxes, checkboxes, etc. work fine, but reference (set) selectors and drop downs don't (at least not in the current version).
You could report this as a bug in the Mendix Partner Portal, and perhaps in the mean time use the second option to achieve something similar?