Hm... I can't explain why this would happen. If your notification is running on a RITM record (sc_req_item) you ought to have access to the Variables object through the condition builder. It works for me in my instance when I test a similar, albeit simplified filter. When the checkbox is unchecked, the Notification does not fire. When the checkbox is checked, the Notification does fire.

What happens when you put some code in the Email Notification to output the values of the variables? Anything unexpected? (see JavaScript in emails )

//obviously, you should replace these variable names with your actual, case sensitive variable names.

gs.info("df: " + current.variables.df + ", corp: " + current.variables.corp);