I've figured out the fix for this. This package uses the very cool DistUtilsExtra.auto module which allows the package to automagically figure out what needs to be done and included in the package. However, the bit of code which looks for kde .ui files searches for files that match *.ui and then checks the first line of the file to see if it starts with:
But unfortunately the first lines of kde/ManagerWindowKDE4.ui are:
<?xml version="1.0" encoding="UTF-8"?>
and therefore it doesn't get picked up. It looks like the current bzr branch for this project has this problem fixed so the next release should work fine.