ProperCase and Word functions don't play well together

I have what appears to be a bug. The scenario is as follows.

I am importing users from a SQL DB the table has the following fields, "First_Name", "Last_Name" and “Known_As”. Unfortunately not all identities have the "Known_As" value captured. Additionally the oorganisation captures user first and second name in the First_Name attribute and all values are captured in uppercase (e.g. John Michael Smith is captured as follows

First_Name = JOHN MICHAEL

Last_Name = SMITH

Known_As =

When I inbound the identity into the FIM portal I use the following custom expression

 IIF(IsPresent(Known_As),ProperCase(Known_As),ProperCase(Word(First_Name,1," ")))

Unfortunately this returns a null value

However, if I use the following custom expression

IIF(IsPresent(Known_As),Known_As, Word(First_Name,1," "))

I get the value for firstname in the portal as JOHN

It would appear to me that the functions propercase and word do not play well together.