Whether this is your problem...
... depends on how your RPi got Raspbian Jessie installed.
AFAICT this is only a problem if you wiped the SD card and installed Jessie from scratch.
I didn't do that. Instead, I tweaked the apt configuration so it pointed at jessie instead of wheezy and then then did an normal upgrade (full procedure described below). If you've done the same, you won't see this problem because the copy of /var/lib/systemd/random-seed that was used by Wheezy is still there and will be used by Jessie when needed.
For those who need it, here's the upgrade procedure I used.
1 Modify the file /etc/apt/sources.list. Change "wheezy" to "jessie" in the first line, so it reads
"deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi"
2 Modify the file /etc/apt/sources.list.d/raspi.list. Change "wheezy" to "jessie" in the first line and add " ui" to the end of that line, so it reads
"deb http://archive.raspberrypi.org/debian jessie main ui"
3 Create the directory /home/pi/.config/autostart by typing "mkdir /home/pi/.config/autostart" in a terminal. (Note the . in front of config.)
4 Type "sudo apt-get update" in a terminal to update the apt index files.
5 Type "sudo apt-get -y dist-upgrade" to start the upgrade process. This will take a couple of hours.
Reboot once the upgrade has finished you will see several messages about "Calling CRDA to update world regulatory domain". Wait until these stop and then login at the command prompt as the pi user. If the GUI doesn't start automatically, type "startx" at the command prompt. The desktop will take several minutes to launch as files are updated; the screen will go black, but just wait for it to finish.
Once the desktop has loaded, open a terminal window and type "sudo apt-get install rc-gui alacarte". This installs the new packages - respectively, the new GUI version of raspi-config and the Alacarte menu editor.