With "strict" and "warnings" on:

Illegal octal digit '9' ignored at ...
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perldiag says:

Illegal octal digit %s ignored (W digit) You may have tried to use an 8 or 9 in an octal number. Interpretation of the octal number stopped before the 8 or 9.

In other words, your character class will include the characters \000 - \000 (that is \000) and "9"