From @masak

<TimToady> m​: ''.substr(5).say
<camelia> rakudo-moar 1acf80​: OUTPUT«(HANDLED) Start argument to
substr out of range. Is​: 5, should be in 0..0; use *5 if you want to
index relative to the end [...]
<TimToady> the *5 is a bug
* masak submits rakudobug
<masak> m​: say "a".substr(7)
<camelia> rakudo-moar 1acf80​: OUTPUT«(HANDLED) Start argument to
substr out of range. Is​: 7, should be in 0..1; use *7 if you want to
index relative to the end [...]

From @lizmat

Fixed with d7698f3de2eb3c326aa , tests needed.

On 30 Apr 2016, at 17​:02, Carl Mäsak (via RT) <perl6-bugs-followup@​perl.org> wrote​:

# New Ticket Created by "Carl Mäsak"
# Please include the string​: [perl #​128039]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl6/Ticket/Display.html?id=128039 >

<TimToady> m​: ''.substr(5).say
<camelia> rakudo-moar 1acf80​: OUTPUT«(HANDLED) Start argument to
substr out of range. Is​: 5, should be in 0..0; use *5 if you want to
index relative to the end [...]
<TimToady> the *5 is a bug
* masak submits rakudobug
<masak> m​: say "a".substr(7)
<camelia> rakudo-moar 1acf80​: OUTPUT«(HANDLED) Start argument to
substr out of range. Is​: 7, should be in 0..1; use *7 if you want to
index relative to the end [...]

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

From @zoffixznet

Thank you.

Tests added in Raku/roast@b4254c2fdd

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