Could you do us the favor of creating a code example that demonstrates the behavior?

I've taken your exact string and created variables and subroutines/constants as needed to provide a definition for everything the string tries to interpolate. Here is what I get:

#!usr/bin/env perl

use strict;
use warnings;
use Term::ANSIColor;

sub colorize {
    my($color, $string) = @_;
    return color($color) . $string . color('reset');
}

use constant COUNTER_STATE_VAR => colorize(bright_blue => '(COUNTER_ST
+ATE_VAR)');
use constant COUNTER_START_VAR => colorize(bright_blue => '(COUNTER_ST
+ART_VAR)');

my $desc         = colorize('bright_green' => '|desc|');
my $context_desc = colorize('bright_green' => '|context_desc|');
my $restart      = colorize('bright_green' => '|restart|');

my $var = <<"HERE";
action=setwpos %u +1 ($desc) ; shift ($context_desc) @{[COUNTER_START_
+VAR]} ; shift ($context_desc) @{[COUNTER_STATE_VAR]} ; eval @{[COUNTE
+R_STATE_VAR]} ( \$counter=@{[COUNTER_STATE_VAR]}; ++\$counter; ) ; ad
+d ($context_desc) @{[COUNTER_START_VAR]} ; add ($context_desc) @{[COU
+NTER_STATE_VAR]} ; assign @{[COUNTER_STATE_VAR]} 0 ; set ($context_de
+sc) $restart
HERE

print colorize(bright_red => "<<<<<\n") . $var . colorize(bright_red =
+> ">>>>>\n");
[download]

...produces...

<<<<<
action=setwpos %u +1 (|desc|) ; shift (|context_desc|) (COUNTER_START_
+VAR) ; shift (|context_desc|) (COUNTER_STATE_VAR) ; eval (COUNTER_STA
+TE_VAR) ( $counter=(COUNTER_STATE_VAR); ++$counter; ) ; add (|context
+_desc|) (COUNTER_START_VAR) ; add (|context_desc|) (COUNTER_STATE_VAR
+) ; assign (COUNTER_STATE_VAR) 0 ; set (|context_desc|) |restart|
>>>>>
[download]

Try running it. It looks better in a terminal that supports color; it's easier to see where the interpolation is happening. And then tell us where you were expecting to see interpolation but failing to get the behavior you would expect. If this snippet doesn't reproduce the error you are seeing, then your sample was inadequate in demonstrating the issue, and you'll need to provide us a self-contained snippet we can run to see it happening.