[perl #130529] [Regression] After giving Seq it's own join method, redo behaves strange in grep

[via RT]

# New Ticket Created by  Christian Bartolomaeus 
# Please include the string:  [perl #130529]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=130529 >


With rakudo commit 3c52aa096c Seq got it's own join method. For some reason
that changed the behaviour of 'redo' in 'grep':

< bartolin> m: my $attempts = 0; say (1..5).grep({if $_ == 3 {$attempts++; redo 
unless $attempts  == 10}; $_}).join("|"); say "looked $attempts times for 
element 3"
< camelia>  rakudo-moar f6303d: OUTPUT«1|2|4|5␤looked 1 times for element 3␤»
< bartolin> star-m: my $attempts = 0; say (1..5).grep({if $_ == 3 {$attempts++; 
redo unless $attempts  == 10}; $_}).join("|"); say "looked $attempts times for 
element 3"
< camelia>  star-m 2016.10: OUTPUT«1|2|3|4|5␤looked 10 times for element 3␤»

Further discussion here: 
https://irclog.perlgeek.de/perl6-dev/2017-01-08#i_13878701