TAC said it will be fixed in 6.1.3.2. The issue is:
"We found the root cause for this issue where the controller is adding variables to URL encoding which breaks the re-direction URL. We had raised this issue to Engineering team and this will fixed on 6.1.3.2 which is not yet released.
However, we have a work around to increase the characters in the range of 2 + (n * 3) characters, e.g. "AB", "ABCDE", "ABCDEFGH". This will make sure the URL encoded info lands on a complete %00 which is a valid URL encoded value."
So, it depends on the length of your SSID. Our SSID that has one character has the problem, but another SSID that is 11 Chars long falls within the 2+(n+3) so that one works.