Openssl and the "(stndin)= " prefix

Recently, I've been playing around with the openssl utility. Doing things like this:

# echo -n 'value' | openssl dgst -sha1 -hmac 'key'

57443a4c052350a44638835d64fd66822f813319



# rpm -qa | grep openssl

openssl-0.9.8e-22.el5_8.3



# cat /etc/redhat-release

CentOS release 5.8 (Final)

Note that I show the version and operating system I'm using. Here's why. Look at the following:

# echo -n 'value' | openssl dgst -sha1 -hmac 'key'

(stdin)= 57443a4c052350a44638835d64fd66822f813319



# rpm -qa | grep openssl

openssl-1.0.0-20.el6_2.5.x86_64



# cat /etc/redhat-release

CentOS release 6.2 (Final)

So on a more recent system, openssl has prefixed it's output with "(stndin)= ".
I'm not finding this particularly helpful for my application.
One workaround, suggested here, is to use sed to remove it, like this:

# echo -n 'value' | openssl dgst -sha1 -hmac 'key' | sed 's/^.*= //'

57443a4c052350a44638835d64fd66822f813319