UPDATE: I may have misunderstood your post, and FIXED is meant as workaround.

---

> Fixed: ( foo {$Q} ) + foo {$t}

no, it's not, because this was what I expected.

> + is treated as the unary operator, so

And it would be binary

use strict;
use warnings;

sub foo (&){ shift->()}
sub baz (&){ shift->()}
sub bar {3}

my ($Q,$t,$res) = (10,3);

sub tst { ( foo {$Q} ) + baz {$t}; }


use B::Deparse;

print B::Deparse->new('-p')->coderef2text(\&tst);

print tst();
[download]

C:/Strawberry/perl/bin\perl.exe -w d:/tmp/pm/sym.pl 
{
    use warnings;
    use strict;
    (foo(sub {
        $Q;
    }
    ) + baz(sub {
        $t;
    }
    ));
}13
[download]

update

FWIW I chose + for an example which at least compiles b/c of the ambiguity.

I originally used / which fails without having any unary meaning (it's seen as the start of a m//)