>>> Modified: sys/i386/isa npx.c
>>> Disabled i586-optimized copyin and copyout again. The fault handler
>>> is still broken - it doesn't restore the floating point state.
>Could this problem result in NaN being produced at wrong places.
No, it causes kernel panics.
>I filled a PR (2142) about it, maybe it could be closed then.
That is much harder to fix. It is caused by the floating point state
not being preserved across signal handlers. There are few, if any,
valid and useful uses for floating point in signal handlers, because
an ANSI signal handler must not make any accesses to a global object
other than assignment to ones of type `volatile sig_atomic_t'. Thus
preserving the state would mainly slow down signal handlers.