I certainly agree that there are no red flags in what you've posted. What happens when you sub the following for your execute command:

my $sth = $self->{sth_get};
$sth->bind_param(1, $session_id) or die "Bind failure:" . $sth->errstr
+;
$sth->execute() or die "Execute failure:" . $sth->errstr;
[download]

I'm also a little curious why the binding failure dies in the DBD code as opposed to bubbling up to the user as a simple execute failure. Not so curious as to go source diving, but still...