DateTime :: createFromFormat无法识别没有前导零的小时数

There's a similar question to this one, but it concerns only minutes and seconds. My question is about hours. Let's assume that we want to parse time in the following format: 63000, 6 = hours, 30 = minutes, 00 = seconds. I think we should do it like this:

$datetime = DateTime::createFromFormat("Gis", "63000");

G = 24-hour format of an hour without leading zeros, i = minutes with leading zeros, s = seconds, with leading zeros

Unfortunately it doesn't work in PHP 7.0.12. The function returns false. If I change the first argument to: "G:i:s" and the second argument to "6:30:00", it returns a correct DateTime object. Am I misunderstanding something here, or is it a bug?