As far as I could see, this _does_ give you the same error in 7.7.
It seems very inconsistent between runs, actually. This is with a freshly built 7.7:
ceylon:7.7 $ ~/pike/7.7/bin/pike Pike v7.7 release 45 running Hilfe v3.5 (Incremental Pike Frontend)
sscanf("^^^^^^^^hello", "%*[]%s", string res) && res;
(1) Result: 0
sscanf("^^^^^^^^hello", "%*[]%s", string res) && res;
(2) Result: 0
sscanf("^^^^^^^^hello", "%*[]%s", string res) && res;
(3) Result: 0
sscanf("^^^^^^^^hello", "%*[]%s", string res) && res;
Error in sscanf format string. HilfeInput:1: HilfeInput()->___HilfeWrapper()