COPY failed: stat /var/lib/docker/tmp/docker-build

Question

I have the following dockerfile snippet:

RUN mkdir sys_libs
COPY sys_lib/vs_log.rb sys_libs/vs_log.rb

The file does exist in the local ./sys_lib folder.

when I attempt to build: get:

COPY failed: stat /var/lib/docker/tmp/docker-builder085599896/sys_lib/vs_log.rb: no such file or directory

Note the folder name referenced in the docker path is the name of the local folder, not the name of the docker folder just created.

I get the same if I do a COPY sys_lib/ sys_libs/

If I make the local and the docker folder the same I get the same thing:

RUN mkdir sys_lib
COPY sys_lib/ sys_lib/

I have tried it with leading./ and without on both sides.

I am out of options. Any ideas?