[key] displays instead of a blank when conditional field is within a fieldset

I have an odd problem. Let's say I have a fieldset, and within the fieldset I have a select field ("show" and "hide" for options)and a text field which conditionally shows or hides based on the select field. It would look something like this:

-field_set
--test_select
--test_textfield

Then in my custom email template I have something like this:

TEST SELECT: %value[field_set][test_select]
TEST FIELD: %value[field_set][test_textfield]

If I set to show everything is fine. If I set to hide, then what I get in my email return is this:

TEST SELECT: hide
TEST FIELD: [test_textfield]

I should get a blank after "TEST FIELD:", but I get "[test_textfield]" with "%value[field_set]" trimmed off. I've played around with a few variations, such as putting the select outside of the fieldset and the text field inside the fieldset. It just doesn't work.