I confirm Todd Taft's report - this is still an issue in 18.04. The whole purpose of having Unison as a Debian/Ubuntu package is to provide the function that Unison is meant for - to allow syncing of files across not only multiple machines, but multiple versions of an o/s and between versions of o/s, current and old. This is not the case with Unison on Ubuntu. It's the death of Unison - eventually - if unison-all does not include support for unison as installed on heterogenous and old hardware, other o/s.
I confirm Todd Taft's report - this is still an issue in 18.04. The whole purpose of having Unison as a Debian/Ubuntu package is to provide the function that Unison is meant for - to allow syncing of files across not only multiple machines, but multiple versions of an o/s and between versions of o/s, current and old. This is not the case with Unison on Ubuntu. It's the death of Unison - eventually - if unison-all does not include support for unison as installed on heterogenous and old hardware, other o/s.