Hm, methinks you only moved the problem:
Pike v7.8 release 263 running Hilfe v3.5 (Incremental Pike Frontend)
string s = "x"*300; strlen(sprintf("%8H", s));
(1) Result: 308
strlen(sprintf("%9H", s));
sprintf: Length of string to %9H too large. HilfeInput:1: HilfeInput()->___HilfeWrapper()
strlen(sprintf("%10H", s));
(2) Result: 310