Files getting regenerated after patches getting applied for busybox

Hi all, I'm new to openwrt , i'm trying to build busybox for openwrt , for this I have some custom patches and I have applied them by passing instruction in the makefile. And in build logs I see that these patches are getting applied, after this some of the files to which i have applied patches are getting regenerated [ I have applied patches to many c and header files but only below mentioned files are getting regenerated I don't know the exact reason why this is happening]
GEN include/applets.h
GEN include/usage.h
GEN miscutils/Kbuild
GEN miscutils/
GEN networking/Kbuild
GEN networking/
GEN networking/udhcp/Kbuild
GEN networking/udhcp/
GEN libbb/Kbuild
GEN sysklogd/Kbuild
GEN sysklogd/

I have tried to verify source Makefile but it's a bit complex for me. Any pointers on this will help.
Thanks in advance.