I had edited your filter function to switch out the field sizes using Bootstrap’s columns for my form, and found that it was replacing the classes of my admin-side Gravity Forms editor. So I added a check to make sure that the admin side always displays exactly what Gravity Forms expects:

https://gist.github.com/rynokins/8089d4d5641edd11fe09cbc50765df7c

(I’m doing all my gform class overrides in SASS with Bootstrap loaded locally, in case you’re wondering why I removed the ‘form-group’ class)

Thanks for your post – really helped me out!