The issue is probably not related to seam (related to facelets themselves), however, I did not try reproducing the issue outside of seam.

Steps to reproduce:
1.) Create new seam project (war)
2.) Open the home.xhtml file (war_project/WebContent/home.xhtml) in the JBoss Tools HTML Editor (the default option)
3.) Modify the file somehow (i.e. change the heading)
4.) Hit ctrl+s to save
5.) Close the tab by clicking the tab's cross.
6.) After the sixth step JBoss Tools freezes and after a while the application crashes. I cannot see any error in the log.