unable to login on some login required pages

Using TorBrowser the IP address regularly changes causing automatic logouts.

The shown login page however does not work. I can enter credentials endlessly and the same login form is shown over and over again.

The only way to login then is to open / and login there.

(Talked about it shortly with azul who said it is known but I could not find it searching for 'login')

This also happens if one visits a link or bookmark that points to a url like /groups/riseup/pages. It works with /riseup/pagename and /