IIRC in that case you can exit the station and re-enter through the correct entrance for free.
> In all the other subway systems I used, you pay your fare and you are free to roam the whole station and reach any track
I've also seen such stations in Paris. I was later told that the ticket works for 30 minutes after first use, so again, you can exit and re-enter just fine.
And St Petersburg has a few of these as terminal stations. Not a problem if you went there intentionally, but it is a problem if you ended up there accidentally, because they are rather strict about not letting people ride the train as it turns around.
> In all the other subway systems I used, you pay your fare and you are free to roam the whole station and reach any track
I've also seen such stations in Paris. I was later told that the ticket works for 30 minutes after first use, so again, you can exit and re-enter just fine.
And St Petersburg has a few of these as terminal stations. Not a problem if you went there intentionally, but it is a problem if you ended up there accidentally, because they are rather strict about not letting people ride the train as it turns around.
edit: I googled it, http://metro.spb.ru/information.html#opl1 explicitly says, with too much legalese, that you have to pay again ¯\_(ツ)_/¯