Distribution Wizard doesn't kick in when upgrading from 4.5.3 to 5.4.1

Steps to reproduce:

1. Setup the XEM 4.5.3 WAR with Jetty/Hsqldb
2. Install the UI with the DW or by importing the corresponding XAR
3. Stop the server and replace the xwiki folder from webapps with the one from the 5.4.1 war
4. Start the server

You'll see the Main.WebHome page without any redirect to DW. Reproduces also on Tomcat/Mysql. Doesn't reproduce when upgrading from 4.5.3 to 5.2.4.