This may be a stupid question, but the problem doesn't exist in 3.0.5 or 813, and a forum search hasn't shed any light on the problem.
Installed 823, created a new project file. Used existing build.xml file. Open the build.xml and there are errors in all my lines.
'name' and 'value' are both red, and when I roll over them I get a pop-up containing "Attribute name is not allowed here", or "Attribute value is not allowed here".
Close 823 and opening the same project file in 813 and all is well. Also, environment variables don't work, and I tried the .MacOSX/environment.plist suggestion.