There is no application preference for this. You will have to disable the option on each file that you dont want it on for.
In other words there's nothing more that can be done
Sorry. I dont think there is.
Just to confirm, "mr_vodka" is correct (Thank you!). There is no application preference for spelling options; only preference by file. That way, you can have a file that allows questionable spellings, and another file that doesn't.