Referencing data type param in alarm custom subj expression

Windows 7 64bit
Ignition 7.8.2

I’m unable to bind parameters to the “Custom Subject” field of the alarm configuration within a UDT.

I have two defined string parameters I’m attempting to bind to an expression in Custom Subject:

{line} + “CCL” + {position} + " ONLINE"

The alarm icon displayed next to the tag within the data structure is immediately “flagged” whenever I attempt to reference a parameter in this field, i.e., simply binding {line} will flag the tag and the console displays the following: