If you start up bitbake in memory-resident mode (. ./oe-init-build-env-memres) and then run bitbake -e | less, you'll notice that in place of the history for each variable there is instead "[no history recorded]".
I've just double-checked and this issue is still present in master as of 81021bc0aa0f64e67535f6a9551e921a64fe4395.
Fix merged to master: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=453835679ba36b2e07f7aa8aa653a8cfeda95675