Just because you did set role does not mean you lost your superuser privileges, it's correct behavior.

If you want to impersonate in a permissions sandbox it's easy:

create role usera_sandbox in group usera;
\c - usera_sandbox
  

-- 
regards,
Kiriakos Georgiou

I feel that set role logic is kindof misleading.

I am a superuser, admin,

I do:

set role usera

Now I am under the security context of usera, so I think running any sql is safe as long as it's allowed by usera.

Which is not the case!

as usera can do:

set role userb; other sql,

or 

reset role; orther sql,

it turns out it's not safe at all, the sql can easily get access right of the super user. it can impernate userb though they do not have any relationship whatso ever.

I really feel, once you "set role usera", you should behave like usera, you should NOT have the power say: hi, I can assume my super user power whenever I want. As this make the "set role usera" pretty much useless.

It's unsafe!