Confusing command in Dockerfile of official docker image

I found the following command in Dockerfile of official docker image (docker history).

chown -R root. ${JIRA_INSTALL_DIR}/

The dot after owner confuses me, I'm surprised that chown accept such input.

GNU coreutils manual:

Some older scripts may still use ‘.’ in place of the ‘:’ separator. POSIX 1003.1-2001 (see Standards conformance) does not require support for that, but for backward compatibility GNU chown supports ‘.’ so long as no ambiguity results. New scripts should avoid the use of ‘.’ because it is not portable, and because it has undesirable results if the entire owner‘.’group happens to identify a user whose name contains ‘.’.

Please replace dot with colon, for sanity.