Maybe there are gremlins in the wiring. :yikes
I don't understand how devices could possibly turn themselves back on. You should be using an X-10 appliance module to turn the receiver on/off. This eliminates power from the power cord.
When you switch it off, it goes CLUNK. A relay opens and the Coolsat 8100 is dead to the world.
What switches it back on? Could your neighbors be using X-10 and you have the same house code? (A - B - C - etc.)
edit,
IIRC, Lamp modules will sense if the lamp is turned on/off at the device and apply power... But you shouldn't use Lamp modules on a STB. Lamp modules are like dimmers. (Only for resistive loads)
No, I never use lamp modules, except for lamps that I want to dim. And no, it's not neighbors, I don't have any neighbors within a half mile.
Like the other responder said, even the appliance modules I have, will turn on if you turn the device off and then back on, and that's what seems to be doing this, ie when the X10 module turns the Coolsat off, apparently the coolsat must be trying to reboot or something with whatever residual power it has, and turns itself off then back on, which then triggers the X10 module to turn back on. It's really weird... you hit the button to turn the thing off, and hear the loud click of the appliance module, then a few seconds later, another loud click, as it turns back on.
One thing that just occurred to me, is that there are two types of those modules, older "dumb" modules, and the newer ones that report their state back over the power lines. Ie I have a program I wrote that will pop up a message on my computer say if house code A, unit 5 turns on or off, and this will happen if you turn a device off and on by it's own switch when the module is off (if I remember right). So maybe the newer modules are sensing the state of the device, and I should try one of the older non-reporting modules.... if I have any. I usually buy the reporting type so that when I use the monitoring program it will work right. It's been a long time since I've done the X10 monitoring, so I may be remembering wrong. This may get me back into that to try to diagnose this Coolsat thing.