I was investigating why a TeamCity build-agent was running out of disk, and found over 11,000 files in /private/var/tmp, all named along the lines of Untitled-<random-unique>.uicatalog.
Each file is at least 0.6MB. The total disk footprint is on the order of 4GB.
The files dated back several months, so they survived reboots.
Who is creating them?