%cp_samp=map {$_} split/:/, $sy;
is the same thing as
%cp_samp=split/:/, $sy;

foreach $sy (@ex_array) { %cp_samp=map {$_} split/:/, $sy; }
is the same thing as
%cp_samp=split/:/, $ex_array[-1] if @ex_array;
which produces neither what you want nor what you said is produced.

Finally, may I recommend a HoA ($cp_samp{sample1}[0]=3 $cp_samp{sample1}[1]=4 ..) instead of a HoH?

my %cp = map { my ($label, $list) = (split(/:/), '');
               $label => [ split /,/, $list ]
             }
         @ex;
[download]

Update: By the way, the for version would be

my %cp;
foreach (@ex) {
   my ($label, $list) = (split(/:/), '');
   $cp{$label} = [ split /,/, $list ];
}
[download]