From cxreg@pobox.com

This happens when you create more than 100% overlap with a negative value in rotor

count@​bumba​:~$ perl6 --version
This is Rakudo version 2015.12-230-g2e17820 built on MoarVM version
2015.12-29-g8079ca5
implementing Perl 6.c.

count@​bumba​:~$ perl6 -e '<a b c>.rotor​: 1 => -2'
RNING​: unhandled Failure detected in DESTROY​:
Index out of range. Is​: -68, should be in 0..Inf
  in block <unit> at -e line 1

WARNING​: unhandled Failure detected in DESTROY​:
Index out of range. Is​: -67, should be in 0..Inf
  in block <unit> at -e line 1

WARNING​: unhandled Failure detected in DESTROY​:
Index out of range. Is​: -66, should be in 0..Inf
  in block <unit> at -e line 1

[...]

From @zoffixznet

Thanks for the report.

Fixed in rakudo/rakudo@4e08af5f04
Tests added in Raku/roast@53bf79d497

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ZZ | https://twitter.com/zoffix

The RT System itself - Status changed from 'new' to 'open'

@zoffixznet - Status changed from 'open' to 'resolved'