That's not what I get nor what I would expect (but this is not in debug mode): 

Win8 Strawberry 5.8.9.5 (32)  Sun 10/11/2020 21:47:54
C:\@Work\Perl\monks
>perl -Mwarnings
my $a=$x=$y=$z = 1;

print "|$a|$x|$y|$z|";
^Z
|1|1|1|1|

Win8 Strawberry 5.30.3.1 (64)  Sun 10/11/2020 21:45:55
C:\@Work\Perl\monks
>perl -Mwarnings
use v5.10;

my $a=$x=$y=$z = 1;

say "|$a|$x|$y|$z|";
^Z
|1|1|1|1|

[download]

Update:

What about

my $a=$x=$y=$z = foo()
With respect to this specific statement: 
Win8 Strawberry 5.8.9.5 (32)  Sun 10/11/2020 21:48:09
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings
use Data::Dump qw(dd);

sub foo { return 9, 8, 7; }

my ($x, $y, $z);

my $a = $x = $y = $z = foo;

dd $a, $x, $y, $z;
^Z
(7, 7, 7, 7)

[download]
Same result under version 5.30.3.1.

Give a man a fish:  <%-{-{-{-<

In reply to Re^3: What's happening in this expression? (Updated) by AnomalousMonk
in thread What's happening in this expression? by zapdos

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