Bash on Windows: mv command - caot move to a subdirectory of itself

I'm trying to install Ruby from sources on the Windows Linux Subsystem. I've successfully built from source in my home directory: ~/ruby/ruby-2.3.0 and I'm trying to move it to /opt/rubies/.

When I run the move command I get the following error:

/# mv ~/ruby/ruby-2.3.0/ /opt/rubies/
mv: caot move ‘/root/ruby/ruby-2.3.0/’ to a subdirectory of itself, ‘/opt/rubies/ruby-2.3.0’

This is super confusing as I'm moving the directory to a totally different location, not a subdirectory of itself, as the paths themselves show.

It does the same thing for any move command under my home directory:

~# mv test/ /
mv: caot move ‘test/’ to a subdirectory of itself, ‘/test’

And I can't seem to copy any files either:

~# cp ruby/ruby-2.3.0/ /opt/rubies/ruby-2.3.0
cp: omitting directory ‘ruby/ruby-2.3.0/’

Am I doing something wrong?