I don't think you want to invoke 'returns' in your grammar. Namely:

  expression : INTEGER OP expression
             { return &::expression(@item) }
             | VARIABLE OP expression
             { return &::expression(@item) }
             | INTEGER
             | VARIABLE
             { return $::VARIABLE{$item{VARIABLE}} }
[download]

Should be the following instead:

  expression : INTEGER OP expression
             { $return = &::expression(@item) }
             | VARIABLE OP expression
             { $return = &::expression(@item) }
             | INTEGER
             | VARIABLE
             { $return = $::VARIABLE{$item{VARIABLE}} }
[download]

Your forced returns may be interfering with code that acknowledges that you've matched something and to move on, which only seems to rear it's head in the print( something ) case.

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
"I can see my house from here!"
It's not what you know, but knowing how to find it if you don't know that's important