Now i thought writing a live ISO to a usb stick made it 100% read only but i've found an interesting but troublesum bug if anyone has a spare USB drive to try and replicate drive corruption.
I done standard refracta ISO write to a corsair USB stick and rebooted with the first standard option.
I opened the software synaptic manager and done a complete removal of YAD for testing , the USB stick done alot of LED flashing which i assumed was just reading the drive but after i had finished i decided to reboot to a fresh session and i was met with just a black screen and a mouse pointer right at the point when normally the desktop would appear and the only option was a hard power down.
It didn't matter how many times i rebooted it was exactly the same so i re-wrote the ISO to USB and rebooted and everything was normal and running perfectly until i done the same again and removed YAD from synaptic and again the same problem of booting to a black screen as before.
The only way i could clear it was to use the boot to text option and then use startx , sometimes i got the same black screen and other times i got the normal desktop back but either way once a boot to text with startx had been done i could then reboot the USB stick to desktop as normal but now with a slight delay of the black screen just before the desktop appears.
Removed YAD yet again from synaptic and then the same problem of booting again to a black screen and the only way to clear it was the same boot to text , startx , shut down and reboot.
Re-wrote the ISO to USB and it was then back to normal with a fast boot straight to desktop until yet again i removed YAD and then got the same exact problem back again.
For confirmation i tried the exact same thing on my other computer with two different brand USB sticks and both gave the exact same problem with a completely new Mint install and a new Refracta snapshot ISO image for that computer.
Now i don't know if this is anything to do with it but both computers have a Nvidia card and i've noticed a lot of messages at startup and shutdown about nvidia-persistenced , it might be nothing to do it but something is being persistence and writing to USB when it shouldn't and corrupting something.
Sorry for the long post but i'm not very good at explaining myself.