After working quite a while with SP now, I found a nasty thing that happened several times to me now:
Being correctly logged in under WP, I start editing a post or PM in SP. Sometimes, this takes a little longer for research aso. When trying to send the post/PN, SP tells me, that I am not allowed to do this and sends me immediately to the login page of SP. No way to go back without login (although WP still says, I am logged in).
After logging in , the whole contents of the edit area is lost and you start from scratch.
Why is SP doing this? At least, a warning could show up so you ar able to copy the content of the editor before logging in again.
Or even better, do not keep different login information than WP!