This is a repeat of bug 724738. It looks like the proposed change to fix this for new securities didn't get committed.
https://github.com/Gnucash/gnucash/pull/1087
Created attachment 374133 [details] GnuCash 4.6 New Security Dialog Uh, wrong. What are you looking at?
Oh, sorry, I misread "save" as "have".
https://github.com/Gnucash/gnucash/commit/621704ebeb2d182be6784ea6602c6fbd3f3b67ce