I also tried creating /root/.joe/jdjd and /root/thing/jdskjd
A reset leaves the file in ".joe" and gets rid of the file in "thing".
So the problem is with removing files in sub-directory which starts with DOT
Your link leads to somebody's own copy of four year old code from 2015 instead of the current version. There may not be that much relevant difference, but still it might be better to look at the actual source repo at https://git.openwrt.org/?p=project/fstools.git;a=tree . At least the overlay code has got lots of new commits since then.