Growing up in ACAD I learned e for erase and ex for extend - and so. I happily customised the keyboard commands in various DCAD versions but the upgrade to v5 there seemed to be a change to only one letter to describe the command (SEKEs I assume) - e can be used for erase but I can't use ex (typing the first e started the erase command).
Not seeing a workaround for this feature I started learning the new way usine e for erase and learning x for extend - only to find one day it had reverted to the old acad way. No worries: "adapt and conquer", eh? I swapped back, but just now, in the same session - no saves, no reboot, no crashes - it swapped from one to the other and back again.
Frustrating of course.
Thoughts or advice? I did find Brians' advice to back up the Customisation file through "Options tab in the customize dialog (Tools | Customize)" and further advice in that post about the def1024acstd.cfg file. I will play with these for a while.