When editing a properties file or an XML file of e.g. 2000 lines, typing IntelliJ 9 goes really, really, slow. Much slower than typing in a .java file.

Could this be a type of inspection, or the syntax highlighting, in these files, or what could it be?

At this time I disabled inspections for both XML and Properties files, and it seems that typing in XML goes ok now, but in Properties files it's still a 1-2 second lag between hitting a key on the keyboard and seeing the result on screen.