50G resets after attempting Erase/Draw function with F'

[Hlib]

Skyblues wrote, post #1:

Quote: When I go back to where I enter an equation (LS hold / Y=) I am getting the following error:

Error:
No Current Equation

From this point, I am not able to return the Plotting functions/Equation Entry where I can Add an equation without getting that error.

Remaining in the current directory, we can return deleted function by pressing "choose" (F4) in "Y=" mode. Or, say Y1, disappeared from "var" in current directory?

Skyblues wrote, post #4:

Quote: Should I try to update my 50g to ROM 2.15 in HPCALC.ORG anyway?

Except mentioned in link (4950_215.bin), I also tested ROM-file 2MB_215f.bin (size 2 080 768 bytes) both in real HP-50G and in android simulator "go49gp_v1.0.6.apk" at the Chinese smartphone. No malfunction noticed. IMO, to be convinced that the calc is without defect, you should upgrade it using SD.
Setting system flag to "-55"=1 (i.e. No last args) does not cause error or reset at my devices. Formula for dF/dx changes to 1. So the calculator builds {Y1(X) 1.}, wich I can see in 2D/3D mode.
But I do not understand: what user flag "55" does in this case and where it works?