How do I determine which .tpl file is my problem from a Smarty error?

[ellmann creative]

I've been having issues with Faceted Navigation added by a theme (the price slider wasn't showing up at all). I enabled dev mode, and was attacked with a Smarty error:

ContextErrorException in smarty_internal_templatebase.php(157) : eval()'d code line 123:Notice: Undefined index: filter_key

- however, I'm having trouble finding out which .tpl file is my issue. I don't see any ".tpl" in the error code anywhere, the only thing I can see is position #3 on the call stack, referencing "content_5aa2c55c580659_85562675(object(Smarty_Dev_Template)) in smarty_internal_templatebase.php on line 188".

Any help would be appreciated.