Found this today.
Had it in Classic, but I don't think it matters.
Put calc in Frac
Goto the Window menu and change at least one of the options so that it has a thick / in it
Change mode to something other than Frac
Open up the Window menu again
Either scroll down to the option with the thick / in it and then press Y=, or scroll one past.
The z address is now 31 instead of 0 (I counted)
The z address can be reset by turning the calc off then on, but so long as the thick / is present in a Window menu option, it can be retriggered by the above scrolling process.
If the calc APDs while the z address is 31, it wipes the graphscreen without marking it dirty, leaving a blank graphscreen that can be restored with a ClearDraw.
The way to fix this is to remove the thick / from the Window options, or put the calc in Frac mode, and turn it off then back on.
We finally figure out the fraction glitch. What happens is a side effect in the universal flash unlock ends up modifying the OS. So what I've done is make a mod to the OS so that even when the flash unlock tries to change it, it will end up having no effect.
In short, run this on OS 2.55 and you won't have to worry about the fraction glitch any more.
Also, by the way this works, it can't happen in 2.53. However, it does occur in 2.43, though I have no idea what the side effect is.
Lol, the answer to the problem is two posts above yours. But, you're on your way to finding more glitches
As a side note, we're trying to get people to use our new universal flash unlock that does not corrupt the OS. This will make this problem less prevalent, but with the large number of deceased programs, my OS patch might be the only cure.