Just to add another anecdotal data point: me neither. Neither in java, nor in .Net, and surely not in C++ (there were lots of other things to mess up), having around ~15 years of experience under my belt. To me it is quite elementary, almost muscle memory, to never mutate objects used as keys - and while I observed quite a few rookie mistakes (some of them from the "I" perspective), it'd never occur to me to change a key in a map.

I'd probably learn a lot from stories explaining the environment of such situations, so if you have one, please share.