I hate to post this to a forum but I don't know of a better way to communicate with IDEA developers.
Tracker Request #23710 "XML Editor: shows element error when everything is okay" was submitted on December 15 but the status has not been moved to open.
This file trips up the XML editor and Ant tag completion won't work:
Build 1071 doesn't seem to handle this. We code many of our Ant scripts this way as a reuse mechanim. It's important for us that IDEA handle this correctly.