to describe this I have to go more into details. My hoster is using the system where all files and directories are owned by a ftp user and the web server only has access via group. Consequently no write access, which should result in wordpress asking me to give ftp credentials for any upload (like media or plugins).
To my delight it doesn't and works perfectly without asking for those credentials - BUT WHY?
The reason I'm asking is that it stopped doing this and now DOES ask for FTP credentials and does not allow any longer media updates. To make it more interesting, this is all bound to one account from my provider. On another I have the same installation and it works there.
I thought maybe it is bound to the update I did last week, but no, another installation of WP which is older (3.7.1) has the same problem.
I read about the file access API of WP and that it finds out about the owner of files and dir and then handles accordingly. I hope somebody knows how it surrounds the usual ftp user trick...