Thanks for digging into this issue! Really appreciated.
I'll look into the configuration files later today.

Update: Mentalist Traceur: You've nailed it in your posts . I've fixed the issue in a test build. There are CONFIG_UNICODE_* entries in the BusyBox 1.18.4 configuration file, which aren't to be found in the old one. I'm now pinning down the exact configuration entry responsible and should have a final fix available later today.

On the installer: I have already a script ready which contains all functions from busybox defined on top by location (DEST_BIN="bunzip2 ..", DEST_SBIN="blkid .." ...) and some for-looping, which checks for existing symlinks/binaries before creating new symlinks. The final goal is to provide a single .deb which both provides the binary and does the symlinking.
I'm also working on an uninstaller which basically checks whether an utility is a symlink and if so, it checks whether the binary links to busybox. If not, it won't remove the symlink. This uninstaller works with the same list of functions defined as in the installer.
Still testing and extending; there mustn't be any corner cases of course!