Using $X produces (?,?) in SQL

[systemsam]

 I have the following statement 

HAVING $X{IN,tag_status,ic_status}

Which produces 

HAVING tag_status IN (?)

when its run against my mysql server

The input control is names correctly - set as Multiselect list of values and has manual values defined as 

Label         Value
Status 0     STATUS0
Status 1     STATUS1

I would expect to get the follow - say if both were select

HAVING tag_status IN (STATUS0, STATUS1)

Any clue as to why that's not evaluating? 

Sam