I am pretty sure you are trying to delete 3 lines, in which you are only reading one line at a time.

I could handle this by putting in a counter:

my $counter = 0;

if ( $_ =~ /unassigned/ ) {
    $_ =~ s/.*\n//gi; #delete unassigned line
    $counter++;    #count will be 1 and will be caught by next if stat
+ement
}
if ( $counter = 1 ) {
    $_ =~ s/.*\n//gi;  #delete next line
    $counter++;    #count will be 2 and will be caught by next if stat
+ement
}
if ( $counter = 2 ) {
    s/.*\n//gi;    #delete the 2nd line after unassigned
    $counter = 0;    #make count to 0 until $_ is something you are lo
+oking for
}
[download]

I dont know how good this will work for your particular problem, but it could give you another way to think about it :)

EDIT: I did not read the rest of the comments, seems there was a better answer already given.