I've tested the Pacth SUPEE-7405 and even tested in Magento 188.8.131.52 to insert Script in the email registration form, and I'm still can do it.
Can you share some more details?
1) How did you install the patch?
2) Did you download it from Magento official site or from some other site?
3) After applying the patch have you verified that the code has been properly affected in the files mentioned in the patch?(I mean whether patch was applied successfully or not?)