As found and reported by Talisam author, apam (HAPPYLND).

sscanf() won't initialize the buffer of the argument passed if the format string is not matched, so when there was no hexadecimal/SMB timezone value, the timezone specified in the ISO date/time string (if any) would be overwritten with 0, converted from the uninitialized 'zone' variable (unlikely to be valid hex-ASCII chars). Thanks apam!