User-defined variable disappears

I’m having trouble with user-defined variables–they keep disappearing on me.

For example, I created a data key called title_sidepanel with a data value of Add New Items. I typed <%UserData title_sidepanel%> into a rectangle on canvas, but instead of the text changing to Add New Items, it completely disappeared. Text will show as long as I type anything other than <%UserData title_sidepanel%>.

Has anyone seen this before? I’m trying to figure out if I’ve done something wrong, but I’m using other user-defined variables in other canvases, and they work just fine. There’s no overlap in data keys between canvases, either. So, I’m at a bit of a loss.