I diddled with it for awhile before doing a groups.google search for "browseentry and balloon helpmsg"

Jack D. figured it out, and you can google yourself for the full discussion, but the gist of it is that BrowseEntry does a GrabGlobal command which mucks things up. Try this:

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::Balloon;
use Tk::BrowseEntry;

# by Jack D. of comp.lang.perl.tk 
my $main = MainWindow->new;

my $be = $main->BrowseEntry(-listcmd=>\&releaseGrab)->pack;
$be->insert("end", "opt1", "opt2", "opt3");

my $sl = $be->Subwidget('slistbox');
my $l  = $sl->Subwidget('scrolled');

my $b = $main->Balloon();

$b->attach($l,
    -balloonposition => 'mouse',
    -msg => ['first entry', 'second entry','third entry']
    );

MainLoop();

sub releaseGrab{
 $main->after(350,sub{$be->grabRelease});
 #  350 ms is the init delay in the balloon 
 # a smaller number will still likely work 
}
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