[perl #125618] Positional capture of separator on ?% operator causes compiler error

[via RT]

# New Ticket Created by  Faye 
# Please include the string:  [perl #125618]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=125618 >


<ShimmerFairy> m: say "ab" ~~ /^ a +% (b) $/
<camelia> rakudo-moar e4077e: OUTPUT«Nil␤»
<ShimmerFairy> m: say "ab" ~~ /^ a *% (b) $/
<camelia> rakudo-moar e4077e: OUTPUT«Nil␤»
<ShimmerFairy> m: say "ab" ~~ /^ a ?% (b) $/
<camelia> rakudo-moar e4077e: OUTPUT«===SORRY!===␤QAST::Block with cuid 
cuid_1_1436969557.11546 has not appeared␤»

On JVM:

<ShimmerFairy> j: say "ab" ~~ /^ a ?% (b) $/
<camelia> rakudo-jvm e4077e: OUTPUT«===SORRY!===␤setcodeobj can only be used 
with a CodeRef␤»

And just to show that it's not just the ?% operator alone contributing to the 
issue, but the capture too:

<ShimmerFairy> m: say "ab" ~~ /^ a ?% [b] $/
<camelia> rakudo-moar e4077e: OUTPUT«Nil␤»