Ruby converts integer to octal-escaped string instead of hex-escaped one. WHY?

I need:

"31ff".scan(/../).map { |x| x.hex.chr }
=> ["1", "\xff"]

But instead I get:

"31ff".scan(/../).map { |x| x.hex.chr }
=> ["1", "\377"]

OK, actually this is just because of:

"ff".hex.chr
=> "\x377"

But I want:

"ff".hex.chr
=> "\xff"

Where is my mistake? What is missing? Environment is HBase shell which is JRuby console.