A RAM Disk uses your PCs memory in a similar way as a regular HDD/SSD. It becomes a storage "volume" like any other, and is assigned a disk letter just like your other drives. So why don't we all use these instead of HDDs and SSDs? For the very reason you saw, RAM memory is not persistent, as soon as power is removed from it, everything on it is lost.
Since a reboot, or even a Windows Restart clears the RAM memory (due to power loss or the standard memory clearing on restart), anything in it will be lost. The RAM Disk will be recreated on each reboot (if configured that way), so anything put there previously will be gone. You may have temporary files or program caches set up on the RAM Disk, but they are just recreated more or less when the RAM Disk is created. So it may appear that some things are still on the RAM Disk, and others are not, but the temporary and cache files have just been created again. That is the major downside of RAM Disks.
Installing programs on a RAM Disk then adds registry settings, file paths and folders, etc, to the limitations of a RAM Disk. The installed files on the RAM Disk are gone after a reboot, but the registry entries, etc, still exist in the OS. That's a mess of course, but reinstall the program on the RAM Disk, and what happens? I'm sure you see what I mean. There may be ways that advanced RAM Disk software deals with all of this, but I don't think that is available on XFast RAM, but I could be missing it.
EDIT: I forgot about the Backup option on the XFast configuration screen, did you try that?
You can experiment with Windows Sleep, and see if everything is preserved on the RAM Disk when the PC wakes. Sleep uses RAM memory to restore the PC to its last state, so is supplied power. I'm not sure what a RAM Disks reaction to Sleep will be, a good question really, I would think it would be preserved, but who knows? I've used RAM Disks on my ASR board, but never really checked that closely.