Expression tag referencing another tag w/ leased scan class

I have an expression tag that is referencing an OPC tag in a udt(both are in the same udt). The OPC tag is in a direct scan class and the expression tag is in a leased scan class that has a slow scan rate of 0. essentially I just want this expression tag to go active when it is subscribed on an active window. It doesnt seem to work if I put the expression tag in a leased scan class. Ive tried this in 7.5.6 and 7.5.9 and it doesnt work in either version.

I guess the first question someone would ask is why would you reference an existing tag. The reason why is because this is a specialized application that runs on the device, and sometimes an outside sensor is used to display the value in this application and other times it comes from existing tags in the device.

What exactly is not working? Are unable to create the tag you are describing or is it not respecting the leased scan class? (Or is it some thing else?)