It does not try to create paths containing tabs, that is just a display issue (but highly confusing). The problem is lack of support for absolute paths (which is fixed by the PR linked above).
Some more details (and an ugly workaround) are documented at:
Basically it requires you to move the extracted directory (probably named “Users” for C:\Users.…) from the current directory to the right location and recompute the cache checksums to avoid reuploading the same cache at the end of the test run.
Another idea is to cache the .cargo directory in the current working directory and attempt to create a symlink from $TRAVIS_HOME/.cargo as relative paths should be handled just fine. Not sure how well that is supported on Windows though.
@BanzaiMan Please consider merging Bash fixes for extracting absolute paths and corrected message prints by Lekensteyn · Pull Request #38 · travis-ci/casher · GitHub, it would allow some ugly hacks to be removed from the .travis.yml files.