Print When Expression

Variable : COMP_LIST_SIZE = 4

I created a text field with a print when expression wherein I use a variable in it like.

$V{COMP_LIST_SIZE}  == 4

this should be printed right? but it is not. I tried putting this in the footer band as well as the detail band and it was showing the field. but when i put this in the header band it does not show this field? what could be wrong?