UDT Instance: Syntax Error on Token 'IDENTIFIER'

I am experiencing strange behavior in 7.8 where a UDT instance created using system.tag.addTag does not allow an string Expression Tag to contain letters, only numbers.

Here is how I create the instance:

Here is the expression tag:

Here are the instance parameters:

Everything is good so far.

Now I add the letter ‘f’ to ClientId parameter:

And here is the instance error:


Nevermind. :scratch: