Why does 127.001 route to 127.0.0.1 and 127.011 route to 127.0.0.9?

FYI: IPv4 will (in theory) insert 0s when they are missing. I used to always use 127.1 in place of 127.0.0.1, but then maybe a decade ago, some tools started throwing errors because they didn't recognize that format.

The place where the "011" issue hits me most is when scripting with day of month, "date +%d" (IIRC), will say "09" on the 9th of the month, which blows up because "9" is not a valid octal number.