bug with large_dir in 5.12.17

There is a bug when enabling large_dir in 5.12.17. I got this during a backup:

index full, reach max htree level :2
Large directory feature is not enabled on this filesystem

So I unmounted, ran tune2fs -O large_dir /dev/device and mounted again. However
this error appeared:

dx_probe:864: inode #576594294: block 144245: comm rsync: directory leaf block found instead of index block

I unmounted, ran fsck and it "salvaged" a bunch of directories. However at the
next backup run the same errors appeared again.

This is with vanilla 5.2.17.