So i made another dump of emunand via D9, and it seems the E9 and D9 dumps are exactly the same size, down to the byte.
I then tried to restore the E9 dump with D9 again:
"ERROR, file is too small!
EmuNAND Restore: failed!"
Then i tried to restore the D9 dump i JUST MADE with D9, and it gave the same error!
Just for reference, when i earlier found out that D9 couldn't restore my E9 dump, i went back into E9 and it restored the dump without complaint. I haven't tried restoring the D9 dump with E9 yet, but i probably don't need to, it seems clear something is borked in D9 at the moment.
I'm using the 20160112 release, btw.
edit: since i don't have a hard mod, i'm not gonna test the sysNand restore in case something goes horribly wrong, but man, i hope it works, since E9 can't restore sysNand at the moment.