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.
*edit*
Sorry for the long post but i'm not very good at explaining myself.