After more investigation this bug appears when shared build of libXaw, libXmu and libXt was enabled in the CVS (http://cvsweb.xfree86.org/cvsweb/xc/config/cf/cygwin.rules.diff?r1=3.26&r2=3.27). Xterm works fine if I build the latest HEAD branch with cygwin.rules rev. 3.26. Now what is the real problem with those libraries ? Any clues will be appreciated. Fabrice.