ADD_WORKDAYS() not working - cannot be converted to CS expression

Similar to these 2 posts for WORKDAYS_BETWEEN():-

http://scn.sap.com/thread/3921319

http://scn.sap.com/thread/3919077

I find that the ADD_WORKDAYS() function is not working in the Calculated Column window when building a graphical CV.

I'm using Studio client 2.2.13 with SPS11 112.02.

Should this be an OSS Note? I don't see anything currently open.