What form design are you using?
I wasn't able to reproduce the problem, but I only found reference to that variable in a few places, so I might have been able to fix it. I've attached a file you can try replacing your version in the users configuration for dreamweaver location:
/Adobe/Dreamweaver CC 2015/en_US/Configuration/Shared/WebAssist/Services/fb_shared_functions.php
Replace it with Dreamweaver closed and then clear the cache.dat file in the Configuration folder and then try again. If that doesn't work I'll need to set up a screen sharing session to debug and fix this with you directly.